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i

UniversityofSouthernQueensland

FacultyofEngineering&Surveying

50kWEddyCurrentbrake50kWEddyCurrentbrake50kWEddyCurrentbrake50kWEddyCurrentbrake

Adissertationsubmittedby

RudolphEdouardBavarin

infulfilmentoftherequirementsof

CoursesENG4111andENG4112ResearchProject

Towardsthedegreeof

BachelorofEngineering(Electrical&Electronic)

Submitted:October,2006



ii

ABSTRACT

The project involves the refurbishment of the “Heenan-dynamometer” located

underneathSblockattheUniversityofSouthernQueensland.

Thecurrentsystemdoesnotallowanycomputerizeddataacquisition.Upgrading

theelectronic control unit using solid state power electronic devices will enable

userstoperformbettertestsonenginesandinthenearfuture,itwillallowtheuser

toacquiredigitaldataviaacomputer.

The actual dynamometer control unit uses valve technology to rectify the AC

sourceandcontrolthesystemoutput.Theupgradedsystemwillperformthesame

operationhoweveriswillusesolidstatedevices.Inordertousethenewsystemon

the dynamometer, a protective circuit based on pre-established conditions has

beendesigned.



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FacultyofEngineeringandSurveying

ENG4111&ENG4112ResearchProject

LimitationsofUse

TheCounciloftTheCounciloftTheCounciloftTheCouncilof theUniversityofSouthernQueensland,itsFacultyofEngineeringheUniversityofSouthernQueensland,itsFacultyofEngineeringheUniversityofSouthernQueensland,itsFacultyofEngineeringheUniversityofSouthernQueensland,itsFacultyofEngineeringand Surveying, and the staff of the University of Southern Queensland, do notand Surveying, and the staff of the University of Southern Queensland, do notand Surveying, and the staff of the University of Southern Queensland, do notand Surveying, and the staff of the University of Southern Queensland, do notaccept any responsibility for the truth, accuracy or completeness of materialaccept any responsibility for the truth, accuracy or completeness of materialaccept any responsibility for the truth, accuracy or completeness of materialaccept any responsibility for the truth, accuracy or completeness of materialcontainedwithinorassociatedwithcontainedwithinorassociatedwithcontainedwithinorassociatedwithcontainedwithinorassociatedwiththisdissertation.thisdissertation.thisdissertation.thisdissertation.Personsusingalloranypartofthismaterialdosoattheirownrisk,andnotatthePersonsusingalloranypartofthismaterialdosoattheirownrisk,andnotatthePersonsusingalloranypartofthismaterialdosoattheirownrisk,andnotatthePersonsusingalloranypartofthismaterialdosoattheirownrisk,andnotattherisk of the Council of the University of Southern Queensland, its Faculty ofrisk of the Council of the University of Southern Queensland, its Faculty ofrisk of the Council of the University of Southern Queensland, its Faculty ofrisk of the Council of the University of Southern Queensland, its Faculty ofEngineeringandSurveyingorthestaffoftheUniversityofSouthernQuEngineeringandSurveyingorthestaffoftheUniversityofSouthernQuEngineeringandSurveyingorthestaffoftheUniversityofSouthernQuEngineeringandSurveyingorthestaffoftheUniversityofSouthernQueensland.eensland.eensland.eensland.This dissertation reportsaneducational exercise and hasnopurposeorvalidityThis dissertation reportsaneducationalexercise and hasnopurposeorvalidityThis dissertation reportsaneducational exercise and hasnopurposeorvalidityThis dissertation reportsaneducationalexercise and hasnopurposeorvalidity

beyond this exercise. The sole purpose of the course pair entitled "Researchbeyond this exercise. The sole purpose of the course pair entitled "Researchbeyond this exercise. The sole purpose of the course pair entitled "Researchbeyond this exercise. The sole purpose of the course pair entitled "ResearchProject"istocontributetotheoveralleducationwithinthestudent’schosendegreeProject"istocontributetotheoveralleducationwithinthestudent’schosendegreeProject"istocontributetotheoveralleducationwithinthestudent’schosendegreeProject"istocontributetotheoveralleducationwithinthestudent’schosendegreepppprogram.Thisdocument,theassociatedhardware,software,drawings,andotherrogram.Thisdocument,theassociatedhardware,software,drawings,andotherrogram.Thisdocument,theassociatedhardware,software,drawings,andotherrogram.Thisdocument,theassociatedhardware,software,drawings,andothermaterial set out in the associated appendicesshould not be used for any othermaterial set out in the associated appendices should not be used for any othermaterial set out in the associated appendicesshould not be used for any othermaterial set out in the associated appendices should not be used for any otherpurpose:iftheyaresoused,itisentirelyattheriskoftheuser.purpose:iftheyaresoused,itisentirelyattheriskoftheuser.purpose:iftheyaresoused,itisentirelyattheriskoftheuser.purpose:iftheyaresoused,itisentirelyattheriskoftheuser.

ProfGBaker

DeanFacultyofEngineeringandSurveying



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CERTIFICATION

I certify that the ideas, designs and experimental work, results, analyses andI certify that the ideas, designs and experimental work, results, analyses andI certify that the ideas, designs and experimental work, results, analyses andI certify that the ideas, designs and experimental work, results, analyses andconclusions set out in this dissertation are entirelymy owneffort,exceptwhereconclusions set out in this dissertation are entirelymyowneffort, exceptwhereconclusions set out in this dissertation are entirelymy owneffort,exceptwhereconclusions set out in this dissertation are entirelymyowneffort, exceptwhereotherwiseindicatedandacknowledged.otherwiseindicatedandacknowledged.otherwiseindicatedandacknowledged.otherwiseindicatedandacknowledged.IfurthIfurthIfurthIfurthercertifythattheworkisoriginalandhasnotbeenpreviouslysubmittedforercertifythattheworkisoriginalandhasnotbeenpreviouslysubmittedforercertifythattheworkisoriginalandhasnotbeenpreviouslysubmittedforercertifythattheworkisoriginalandhasnotbeenpreviouslysubmittedforassessmentinanyothercourseorinstitution,exceptwherespecificallystated.assessmentinanyothercourseorinstitution,exceptwherespecificallystated.assessmentinanyothercourseorinstitution,exceptwherespecificallystated.assessmentinanyothercourseorinstitution,exceptwherespecificallystated.

RudolphEdouardBavarin

StudentNumber:0050001428

______________________________

Signature

______________________________

Date



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ACKNOWLEDGMENTS

Thisprojectwouldnothavebeenpossiblewithouttheinvolvement,assistanceand

moralsupportfromseveralpeople.

Iwouldliketothankmysupervisor,TonyAhfockforprovidingmewithguidance

andknowledgethroughouttheyear.

Iwouldalsoliketothankstheelectricalandmechanicaltechniciansfortheirhelp

withrespecttothepracticalsideofthisproject.

RudolphBAVARIN


November2006



vi

TABLEOFCONTENTS

AbstractAbstractAbstractAbstract........................................................................................................................................................................................................................................................................................................................................................................................................................................................................iiiiiiii

CertificationCertificationCertificationCertification............................................................................................................................................................................................................................................................................................................................................................................................................................................iviviviv

AcknowledgmentsAcknowledgmentsAcknowledgmentsAcknowledgments ........................................................................................................................................................................................................................................................................................................................................................................................................vvvv

TableofContentsTableofContentsTableofContentsTableofContents........................................................................................................................................................................................................................................................................................................................................................................................................vivivivi

ListofFiguresListofFiguresListofFiguresListofFigures ............................................................................................................................................................................................................................................................................................................................................................................................................................ixixixix

ListofTablesListofTablesListofTablesListofTables....................................................................................................................................................................................................................................................................................................................................................................................................................................xixixixi

Chapter1Chapter1Chapter1Chapter1– –– –INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION ................................................................................................................................................................................................................................................................................................................................ 1111

1.1Justificationfortheproject................................................................................. 1

1.2Projectaimandobjectives ................................................................................ 1

1.3Dissertationoutline............................................................................................ 3

Chapter2Chapter2Chapter2Chapter2– –– –BASICPRINCIPLESBASICPRINCIPLESBASICPRINCIPLESBASICPRINCIPLES............................................................................................................................................................................................................................................................................................................ 4444

2.1Dynamometer.................................................................................................... 4

2.1.1Dynamometerclassification..................................................................... 4 2.1.2TheHeenan-dynamometer...................................................................... 5

2.2Electromagneticprinciple ................................................................................ 10 2.2.1Themagneticfieldofacurrentcarryingconductor ................................ 10 2.2.2Eddycurrent .......................................................................................... 13 2.2.3Electromagneticbrakingeffect............................................................... 15

Chapter3Chapter3Chapter3Chapter3– –– –RECTIFICATIONRECTIFICATIONRECTIFICATIONRECTIFICATION ........................................................................................................................................................................................................................................................................................................................ 16161616

3.1Thepowerdiodeorrectifierdiode ................................................................... 16

3.2TheThyristororSiliconControlledRectifier(SCR) ......................................... 17

3.3Rectifiersconfigurations.................................................................................. 21

3.3.1Halfandfullwaverectification ............................................................... 21

3.3.2Halfandfullycontrolledrectifier............................................................. 26

3.4Testingonphasecontrolledrectifier................................................................ 26

3.4.1Thehalfcontrolledbridgerectifier.......................................................... 27 3.4.2Fullycontrolledhalfwaverectifierwithafreewheelingdiode................ 31

Chapter4Chapter4Chapter4Chapter4– –– –TESTANDDESIGNTESTANDDESIGNTESTANDDESIGNTESTANDDESIGN .................................................................................................................................................................................................................................................................................................... 33333333

4.1Inputandoutputlocation ................................................................................. 33

4.2Preliminarytests.............................................................................................. 34



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Chapter5Chapter5Chapter5Chapter5– –– –PROTECTIVESYSTEMPROTECTIVESYSTEMPROTECTIVESYSTEMPROTECTIVESYSTEM ............................................................................................................................................................................................................................................................................ 39393939

5.1Theexistingprotectionsystem........................................................................ 39

5.1.1Thewaterpressureandignitionswitches.............................................. 40 5.1.2Theconnectionsofthecoilignitionengine ............................................ 41 5.1.3ResettingtheDPCOrelay...................................................................... 41 5.1.3Overspeedcontrol ................................................................................ 42

5.2Upgradedprotectionsystem............................................................................ 42

5.2.2Overspeedingprotectiondevice ........................................................... 43 5.2.3Resettingtheinitialstateofthecircuit.................................................... 46 5.2.4Protectivecircuitconfiguration............................................................... 47

Chapter6Chapter6Chapter6Chapter6– –– –THEUPGRADEDSYSTEMTHEUPGRADEDSYSTEMTHEUPGRADEDSYSTEMTHEUPGRADEDSYSTEM........................................................................................................................................................................................................................................................ 48484848

6.1Thehalfcontrolbridgerectifier ........................................................................48

6.1.1ACtoDCconverter................................................................................ 48 6.1.2FiringmodulefortheP102W ................................................................. 51

6.2Upgradedsystem:Manualtorquecontrol........................................................ 53

6.3Laboratorytestingontheupgradedsystem ....................................................55

6.4ThenewcontrolunitoftheHeenandynamometer .......................................... 58

6.5Testonthedynamometer................................................................................ 59

Chapter7Chapter7Chapter7Chapter7– –– –OPENLOOPANDCLOSELOOPOPENLOOPANDCLOSELOOPOPENLOOPANDCLOSELOOPOPENLOOPANDCLOSELOOP.................................................................................................................................................................................................................... 60606060

7.1Theopenloopsystems ................................................................................... 60

7.2Thecloseloopsystem.....................................................................................61

7.2.1Thereferencesignal .............................................................................. 63 7.2.2Thefeedbacksignal.............................................................................. 63 7.2.3Thedifferenceamplifier .........................................................................64 7.2.4PIDController ........................................................................................ 65

Chapter8Chapter8Chapter8Chapter8– –– –DISCUSIONANDCONCLUSIONDISCUSIONANDCONCLUSIONDISCUSIONANDCONCLUSIONDISCUSIONANDCONCLUSION.................................................................................................................................................................................................................... 67676767

8.1AchievementofObjectives.............................................................................. 67

8.2FurtherWork ...................................................................................................68

8.3Conclusion ...................................................................................................... 69

LISTOFREFERENCESLISTOFREFERENCESLISTOFREFERENCESLISTOFREFERENCES .................................................................................................................................................................................................................................................................................................................................................... 70707070

IIIIIIIIIIII APPENDICAPPENDICAPPENDICAPPENDICIEIEIEIESSSS

APPENDIXAAPPENDIXAAPPENDIXAAPPENDIXA– –– –PROJECTSPECIFICATIONPROJECTSPECIFICATIONPROJECTSPECIFICATIONPROJECTSPECIFICATION ............................................................................................................................................................................................................................ 72727272

APPENDIXBAPPENDIXBAPPENDIXBAPPENDIXB– –– –M3MVRDATASHEETM3MVRDATASHEETM3MVRDATASHEETM3MVRDATASHEET................................................................................................................................................................................................................................................................ 74747474

APPENDIXCAPPENDIXCAPPENDIXCAPPENDIXC– –– –P102WDATASHEETP102WDATASHEETP102WDATASHEETP102WDATASHEET.................................................................................................................................................................................................................................................................... 76767676



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APPENDIXDAPPENDIXDAPPENDIXDAPPENDIXD– –– –AFM11DATASHEETAFM11DATASHEETAFM11DATASHEETAFM11DATASHEET .................................................................................................................................................................................................................................................................... 83838383

APPENDIXEAPPENDIXEAPPENDIXEAPPENDIXE– –– –EQUIPEMENTCOSTEQUIPEMENTCOSTEQUIPEMENTCOSTEQUIPEMENTCOST........................................................................................................................................................................................................................................................................ 86868686

APPENDIXFAPPENDIXFAPPENDIXFAPPENDIXF– –– –CONTROLUNITBOXDESIGNCONTROLUNITBOXDESIGNCONTROLUNITBOXDESIGNCONTROLUNITBOXDESIGN............................................................................................................................................................................................................ 88888888



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LISTOFFIGURES

Figure2.1:Dynamometercrosssection ................................................................ 6

Figure2.2:Controldeskofthedynamometer........................................................ 8

Figure2.3:Torquevs.speedcurve ....................................................................... 9

Figure2.4:Magneticfieldofapermanentmagnet .............................................. 10

Figure2.5:Magneticfieldofacurrentcarryingconductor................................... 11

Figure2.6:Magneticfieldaroundasolenoid ....................................................... 11

Figure2.7:Magneticfieldgeneratedwithinthedynamometer ............................ 12

Figure2.8:Magneticfluxdensitythroughtherotor.............................................. 14

Figure3.1:Diodecircuitsymbol .......................................................................... 16

Figure3.2:Idealiseddiodecharacteristic ............................................................ 17

Figure3.3:Thyristorcircuitsymbol...................................................................... 17

Figure3.4:Typicalthyristorcharacteristic ........................................................... 18

Figure3.5:Halfcontrolledhalfwaverectifier....................................................... 19

Figure3.6:Gatetriggercontrolcircuitandwaveforms ........................................ 20

Figure3.7:Sinusoidalwaveform ........................................................................ 21

Figure3.8:Halfwaverectification........................................................................ 22

Figure3.9:Rectifiercircuitwithonediode........................................................... 22

Figure3.10:Fullwaverectification ...................................................................... 23

Figure3.11:DiodeBridgerectifier ....................................................................... 24

Figure3.12:Flowofcurrentduringpositivecycle................................................ 24

Figure3.13:Flowofcurrentduringnegativecycle .............................................. 25

Figure3.14:Halfcontrolledbridgerectifier(SCRserie) ...................................... 26

Figure3.15:Halfcontrolledbridgerectifier(SCRparallel) .................................. 27

Figure3.16:Halfcontrolledbridgerectifieroutput............................................... 28

Figure3.17:fullycontrolledhalfwaverectifieroutput.......................................... 31

Figure4.1:Externalwiringconnectionofthedynamometer................................ 33

Figure4.2:SignalobtainedacrossconnectionC1andC2.................................. 36



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Figure4.3:SignalobtainacrossconnectionA1andA2 ...................................... 37

Figure4.4:Linearitybetweentheoutputvoltageandspeed ............................... 38

Figure5.1:Existingprotectivecircuit ................................................................... 39

Figure5.2:DoublePoleDoubleThrowrelay(DPDT).......................................... 41

Figure5.3:Overspeedprotectionusedwithinitialdesign................................... 43

Figure5.4:M3MVRandfrontpanel.................................................................... 44

Figure5.5:Timingdiagramforovervoltagemonitoring ...................................... 45

Figure5.6:M3MVR ............................................................................................. 46

Figure5.7:DPCO-5532....................................................................................... 46

Figure5.8:Protectivecircuit ................................................................................ 47

Figure6.1:P102Wmodule ................................................................................. 48

Figure6.2:Internalbridgerectifierconfiguration ................................................. 49

Figure6.3:Heatsink ........................................................................................... 51

Figure6.4:AFM-11.............................................................................................. 51

Figure6.5:Controloptionforterminal5,4and3 ................................................. 52

Figure6.6:5kΩpotentiometer........................................................................... 52

Figure6.7:Transformer....................................................................................... 53

Figure6.8:Upgradedcontrolunitsystem............................................................ 54

Figure6.9:Electronicinputpanel ........................................................................ 55

Figure6.10:Testingconfigurationoftheupgradedsystem................................. 55

Figure6.11:Upgradedrectifieroutput ................................................................. 56

Figure6.12:Protectioncircuittestedwithinthelaboratory ................................. 57

Figure6.13:Upgradedcontrolunit ...................................................................... 58

Figure7.1Openloopsystem............................................................................... 60

Figure7.2:Blockdiagramthecloseloopsystem ................................................ 62

Figure7.3:Triggeringmoduleoutput................................................................... 63

Figure7.4:Differentialamplifierconfiguration ..................................................... 64

Figure7.5:PIDcontroller.................................................................................... 65



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LISTOFTABLES

Table4.1:Tachogeneratoroutputvoltageatacertainspeed...............................38

Table6.1:P102Wratingsandcharacteristics .......................................................49

Table6.2:ThermalandmechanicalspecificationoftheP102Wmodule..............50



1

CHAPTER1–INTRODUCTION

1.11.11.11.1JustificationfortheprojectJustificationfortheprojectJustificationfortheprojectJustificationfortheproject

Adynamometerisaninstrumentusedtomeasurethedrivingtorqueofarotating

devicecoupledtoit.Thecompletedynamometersystemconsistsofarotormade

of a high-permeable magnetic material which is enclosed within a stator. To

measure the torque generated byany rotating device coupled to the rotor, the

stator is held in position by a force transducer which measures the force

generatedby theengine.Inordertoloadtheengine, thedynamometerneedsa

DCsourcetoexcitethestatorcoilandgenerateasteadymagneticfield.

TheactualdynamometerusesvalvetechnologytoconvertACtoanadjustable

DCsource.Thetechnologyisobsoleteandthedynamometercontrolcircuithasto

be upgraded. The valve rectifier will be replaced using solid state power

electronic. To protect the dynamometer against overheating and the engine

againstoverspeeding,anupgradedprotectivecircuitwillbedesigned.Theareaof

research for this project is limited to the design of solid state rectifier and an

understandingofmagneticprincipleinvolvedinthedynamometermechanism.

1.2Projectaima1.2Projectaima1.2Projectaima1.2Projectaimandobjectivesndobjectivesndobjectivesndobjectives

The University of Southern Queensland has a “Heenan-Dynamatic”

Dynamometer, type G.V.A.L which uses valve technology to control the

dynamometer.Theactual control unit enablesmanualandautomatic controlof

theload.



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These twodifferentmodesofoperationareobtained througha selector switch.

When the switch is positioned on “governed engine”, the load is manually

controlled.Onacontrary,whentheswitchispositionedon“Ungovernedengine”

engine,speedstabilisationisachieved.

Thisstudyfocusesonthefirstmodeofoperationwheremanualcontroloftheload

isachievedusingsolidstatedevice.

Specificprojectobjectiveswere:

• Researchanddocumentthebasicprinciplesofthedynamometer.

• Familiarizewiththeexistingdynamometer.

• Carryouttestsontheexistingdynamometerthatwillhelpwiththedesignof

thenewDCsupply.

• Design the new DC supply considering requirements such as open-

loop/close-loopspeedcontroloption.

• ConstructtheDCpowersupplyandtesttheupgradedsystem.



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1.3Dissertationoutline1.3Dissertationoutline1.3Dissertationoutline1.3Dissertationoutline

Chapter 2givesabrief overviewofhowdynamometersaregenerallyclassified

andbrieflydescribesthe“Heenandynamometer”.Italsooutlinesthefundamental

principleinvolvedintheprocessusedbytheeddycurrentdynamometer.

Chapter 3 gives an overview of rectifier using solid state devices and

demonstrates by means of experiments, the basic principles involved in half

controlledrectification.

Chapter 4 describes the testing procedure used to locate the input and output

connections of the valve rectifier. Italsodefines themain characteristic of the

tachogeneratorwhichislocatedonthedynamometershaft.

Chapter 5 explains the use of a protective circuit and briefly describes the

protective system used with the valve rectifier. Following that, it gives a

descriptionoftheselecteddevicesusedintheupgradedprotectioncircuit.

Chapter6introducestheselecteddevicesusedforhalfcontrolledrectificationand

describestheoperationoftheupgradedsystem.

Chapter7describestheopenloopconfigurationoftheupgradedcontrolunitand

brieflyexplainshowfeedbackcontrolcanbeachieved.



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CHAPTER2–BASICPRINCIPLES

Thischaptergivesabriefoverviewofhowdynamometersaregenerallyclassified

andbrieflydescribesthe“Heenandynamometer”.Italsooutlinesthefundamental

principleinvolvedintheprocessusedbytheeddycurrentdynamometer.

2.1Dynamometer2.1Dynamometer2.1Dynamometer2.1Dynamometer

2.1.1Dynamometerclassification2.1.1Dynamometerclassification2.1.1Dynamometerclassification2.1.1Dynamometerclassification

Dynamometers are electro-mechanical instruments used to place a controlled

mechanicalloadonrotationaldevices.Basicallythistypeofmachineisusedto

measure the generated power by the engine coupled to it. At the same time,

dynamometersarealsousedforseveraltestingproceduresthathelptodefinean

engine’s characteristics and performance (Winther 1975). For example a

dynamometercanbeuseto testengineenduranceanddetermineitsfatigue life

under permanent stress conditions. From analysis of the results, preventive

maintenance schedules can be organized to maintain good engine running

conditions.

With most of the dynamometer, the torque-speed curves of the motor can be

plotted,andtheirmotordrivescanbetestedoveranintendedoperatingrange.

Whendynamometersareusedtodeterminethetorqueandthepowerrequiredto

operateacoupledenginetoit,theyaregenerallyclassifiedasmotoringordriving

dynamometer. Similarly, when they are driven by a rotating device they are

classifiedasanabsorptiondynamometer.



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In addition to the previous classification, dynamometers can be classified as

enginedynamometerwhere the engineiscoupled directly onto theshaft of the

dynamometer, or they can be classified as chassis dynamometers where the

powerismeasuredthroughthepowertrainofthevehicle.Finally,dynamometers

areclassifiedbythetypeofabsorptionunitorabsorber/driverthattheyuse.Some

units that are capable of absorption can only be combined with a motor to

constructanabsorber/driveroruniversaldynamometer(Winther1975).

Typesofabsorption/driverunits

• Waterbrake(absorption)

• Fanbrake(absorption)

• Electricmotor/generator(absorbordrive)

• MechanicalfrictionbrakeorPronybrake(absorption)

• Hydraulicbrake(absorption)

• Eddycurrentorelectromagneticbrake(absorption)

2.1.2TheHeenan2.1.2TheHeenan2.1.2TheHeenan2.1.2TheHeenan----dynamometerdynamometerdynamometerdynamometer

The dynamometer used for this project has been made by Heenan & Froude

limited.TheHeenan dynamometer typeG.V.A.L represented in figure2.1uses

the eddycurrentbraking principle toapply a controlled load to the engine and

measurethetorquegeneratedbytheengine.



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Themachineconsistsofanabsorptionunitcalledthestatorwhichiscarriedupon

ballbearingssothatitisfreetoswivelwhenbrakingoccurs.Thetorquearmis

connectedtothestatorandaweightingscaleispositionedsothatitmeasuresthe

forceexertedbythestatorinattemptingtorotate.Thetorqueistheforceindicated

bythescalesmultipliedbythelengthofthetorquearmmeasuredfromthecenter

ofthedynamometer.Therotorwhich isinsidethestatoriscoupledtothetested

engine and is free to rotate at any speed depending on the dynamometer

operatingmode.

Figure2.Figure2.Figure2.Figure2.1111:Dynamometercrosssection:Dynamometercrosssection:Dynamometercrosssection:Dynamometercrosssection

(Dynamometerhandbook)



7

(1) Rotor (6) Statorinnerrings

(2) Mainshaft (7) Statorendcover

(3) Halfcoupling (8) Statortrunnionbearing

(4) Mainshaftbearing (9) FieldCoil

(5) Stator (10) GovernorGenerator

For the braking process to occur, the dynamometer is securely bolted to

substantial foundation.This assures steady running andeliminatesmost of the

vibrationsgeneratedbythesystem(dynamometerhandbook).

• Coolingsystem

Theeddycurrentinducedintheinnerringsofthestatorgeneratesheatwhilethe

rotorismoving.Theheatcausedbytheeddycurrentiscooledwithwater.Water

isadmittedtothegapbetweentherotorandstatorandemergesthroughportsat

thebottomofthemachine(dynamometerhandbook).Toassurethattemperature

controlismaintainedwhilethesystemisrunning,awaterpressuresensorswitch

has been included within the water cooling system. If failure of water supply

occurs,theswitchopenstheprotectivecircuitandthusshutsdowntheengine.In

orderfortheinnerringstobecooledefficientlythequantityofwatersuppliedto

thedynamometermustbesufficient.Therefore,if thewaterpressurefallsbelow

anadjustablepre-setvaluethewaterpressureswitchwillopen.

• Measuringthespeed

Thetachometerusedinthesystemisclassifiedasatachogenerator.Thereare

twotypesoftachogenerators,theACgeneratorswhichareusedwiththeactual

systemandtheDCgenerators.ACgeneratorsconverttheshaftrotationalspeed

intoananaloguevoltagesignal.



8

Oneofthemaincharacteristicsoftachogeneratorsis tooutputavoltagethat is

proportionalinamplitudeandfrequencytotherotationalspeed.Thegeneratoris

mounted onto the dynamometer shaft. The output of the generator is

approximately2voltsper100r.p.m(dynamometerhandbook).

.

• Thecontroldesk

Thiscontrolunit has been built withina sheetsteel control deskand is free to

move at any distance from the dynamometer. This control unit is designed to

operatefromasinglephaseACsource.Locatedonthetopofthecontroldeskis

ther.p.mindicatingdialconnectedtothetachometer.

Figure2.2:ControldeskofthedynamometerFigure2.2:ControldeskofthedynamometerFigure2.2:ControldeskofthedynamometerFigure2.2:Controldeskofthedynamometer

• GovernedandUngovernedoption

TheactualelectroniccontrolsystemisarrangedtoprovideaD.C.voltagerectified

fromanA.C.mainssupply.Thecontrolunithasbeendesignedtoproducetwo



9

desired torque/speed dynamometer characteristic under specific running

conditions.Whenthesystemisrunningunder“governed”conditions,itprovidesa

constantD.C.currentwhichflowsthroughthecoilirrespectivetoanyspeedriseof

the rotor. With this arrangement the dynamometer has a natural torque/speed

characteristicasdepictedinfigure2.3.

Figure2.3:Figure2.3:Figure2.3:Figure2.3:TTTTorquevs.speedorquevs.speedorquevs.speedorquevs.speedcurvecurvecurvecurve


Whensetforagivencurrent,thetorquerisessteeplyandthenbecomesconstant

irrespectiveoffurtherspeedincrease.Whilethesystemrunsunder“ungoverned”

conditions, the speed of the engine is stabilised. No current flows within the

system until the speed has reached the controller preset value. Under this

conditionany increaseof the enginespeed is immediately counteracted byan

increase of dynamometer load and if the engine speed drops, it will be

counteractedbyacorrespondingdropinthedynamometerload.



10

2.2Electromagneticprinciple2.2Electromagneticprinciple2.2Electromagneticprinciple2.2Electromagneticprinciple

UnderstandingthemechanisminvolvedwithintheHeenan-dynamometerrequires

an understanding of the electromagnetic concepts applied to it. A permanent

magnet has a natural magnetic field around it, as depicted in figure 2.4. The

magnetic field, or field of influence, can be virtually represented by lines of

magneticflux.Thoselinesarecompletelyclosedcurved,haveadefinitedirection

andareperfectlyelastic(Sharma2005).

Similarly, electromagnets generate a magnetic field with the same properties;

howeverthelatterreliesonelectriccurrenttogenerateitsfieldofinfluence.

Figure2.4:MagneticfieldofapermanentmagnetFigure2.4:MagneticfieldofapermanentmagnetFigure2.4:MagneticfieldofapermanentmagnetFigure2.4:Magneticfieldofapermanentmagnet

(Source:http//www.geocities.com)

2.2.1T2.2.1T2.2.1T2.2.1Themagneticfieldofacurrentcarryingconductorhemagneticfieldofacurrentcarryingconductorhemagneticfieldofacurrentcarryingconductorhemagneticfieldofacurrentcarryingconductor

When direct current is applied to a piece of conductor it generates a steady

magneticfieldaroundit.



11

Asrepresentedinthefigure2.5,thesurroundingfieldisgenerallyrepresentedby

concentriccircleslyingonaplaneperpendiculartotheconductor.

Figure2.5:MagneticfieldofacurrentcarryingconductorFigure2.5:MagneticfieldofacurrentcarryingconductorFigure2.5:MagneticfieldofacurrentcarryingconductorFigure2.5:Magneticfieldofacurrentcarryingconductor

(Source:http//www.bibleocean.com)

Whentwodirectcurrentsflowinginthesamedirectionareappliedtotwoparallel

conductorsclose toeachother, theflux linescombine,and thetwoconductors

attracteachother.

However,whentwodirectcurrentsflowingintheoppositedirectionareappliedto

twoparallelconductorsclosetoeachother,thefluxlinesarecrowdedtogetherin

thespacebetweentheconductor,andthetwoconductorsrepeleachother.Thus,

when a direct current is applied to a solenoid, a magnetic field similar to the

permanentmagnetmagneticfieldisgeneratedasillustratedinfigure2.6.

Figure2.6:MagFigure2.6:MagFigure2.6:MagFigure2.6:Magneticfieldaroundasolenoidneticfieldaroundasolenoidneticfieldaroundasolenoidneticfieldaroundasolenoid

(Source:http//www.schools.wikia.com)



12

The direction of flux line is defined by the right hand thumb rule. When the

solenoidisheldin therighthandsothatthefingerspointsinthedirectionof the

currentflow,thethumbpointstothenorthpoleofthesolenoid.Similarly,whena

direct current runs trough thedynamometer coil, amagnetic field isgenerated.

Figure2.7representsthesteadymagneticfieldgeneratedbytheconcentriccoil

withinthestatorofthedynamometer.

Figure2.7:MagneticfieldgeneratedwithinthedynamometerFigure2.7:MagneticfieldgeneratedwithinthedynamometerFigure2.7:MagneticfieldgeneratedwithinthedynamometerFigure2.7:Magneticfieldgeneratedwithinthedynamometer

Whencurrentis flowingthrough the dynamometer’scoilamagnetomotiveforce

(m.m.f ) also called a magnetic potential is created. Them.m.f produces the

primarymagneticfieldsofthesystemandisgivenbyequation(2.1).Them.m.f is

proportionaltothecurrentandthenumberofturnofthesolenoid.

N I f mm ... = (Ampere-turns) (2.1)

Nisthenumberofturnsofthecoil,Iistheamountofcurrentflowingthroughthe

coil.

Innerrings



13

In the dynamometer system the number of turns is fixed, consequently the

magnetomotiveforcewillonlybeproportional to theamountofcurrentthrough

thesolenoid.

2.2.2Eddycurrent2.2.2Eddycurrent2.2.2Eddycurrent2.2.2Eddycurrent

When a moving magnetic field intersects a conductor, or a moving conductor

intersects a magnetic field, current is induced. The relative motion causes a

circulatingflowofelectronswithintheconductor.Thesecurrents,alsocallededdy

currents or Foucault currents, create electromagnets with magnetic fields that

opposethechangeintheprimarymagneticfield.

Them.m.f generatedbytheseeddycurrentsisproportionaltothestrengthofthe

originalmagneticfield,andalsotothespeedatwhichthemagneticfieldorthe

conductor ismoving.Theseeddy currentsare induced to the inner ringsof the

stator(seefigure2.7)whentherotorstartsspinningwithinthemagneticfield.The

rotorisofhighpermeabilitysteelandmakeswiththestatorthemagneticcircuitof

thesystem.Becauseofthisproperty,thefluxlinesareuniformlyconcentratedat

the rotor pole tips to take full advantageof the available area.Asa result, the

density of the magnetic flux is not the same all around the rotor. Figure 2.8

illustratestherotorpoletipsandtheconcentrationofthemagneticfluxduetothe

magneticpropertyoftherotor.

Thefluxdensityisavectorquantity,anditsmagnitudeisgivenbyequation(2.2).

IntheSIsystemtheunitofthemagneticfluxdensityisWeberpermetersquare.

A B

Φ= )/( 2mWb (2.2)

Atthepoletipsoftherotorthedensityofthemagneticfluxislargebecausethe

fluxesaresquashedintoasmallarea.Everywhereelseontherotorthemagnetic

fluxdensitywillbeweaker.



14

Fluxline

Figure2.8Figure2.8Figure2.8Figure2.8::::MagneticfluxdensitythroughtherotorMagneticfluxdensitythroughtherotorMagneticfluxdensitythroughtherotorMagneticfluxdensitythroughtherotor

Becauseofthesteadynatureofthemagneticfield,therotorwillnotbeaffectedby

anychangeofmagneticfluxdensity.Thereforenocurrentwillbeinducedonthe

rotor.However,whiletherotorismoving,theinnerringsofthestatoraresubject

toachangeinmagneticfielddensity.

According to Faraday’s law, whenever there is a relative motion between a

conductorandamagneticfield,anelectromotiveforceisinducedintheconductor

andisproportionaltotherateofchangeatwhichthefieldiscut(Sharma2005).In

this case, the inner rings are held stationary and they are subject to varying

magnetic fields produced by the rotation of the slotted rotor within the primary

magnetic field.Theseelectromotiveforcesare localizedwiththe innerringsand

generateeddycurrentsduetotheresistivenatureofthematerial.Fleming’sRight

handrulecanbeusedtodefinethedirectionoftheinducedelectromotiveforce.

However, inaccordance toLenz’s law, representedbyequation (2.3), theeddy

currentswillalwaystendtoopposethechangeinfieldinducingit.

t N emf

∆

∆−=

φ (2.3)

WhereNisthenumberofturnandt ∆

∆φ isthechangeinfluxwithrespecttotime.



15

2.2.3El2.2.3El2.2.3El2.2.3Electromagneticbrakingeffectectromagneticbrakingeffectectromagneticbrakingeffectectromagneticbrakingeffect

Themagneticfieldscreatedbytheinducededdycurrentarecalledthe secondary

magnetic fields and they attempt to cancel the magnetic field causing it. This

phenomenon generates new forces within the dynamometer. One force which

actsuponthestatorandanotherforcewhichopposesthefirstactsupontherotor,

andthusdecelerateitsmotion.

The forceacting upon the stator forces it torotate in the samedirectionas the

rotation of the rotor. The absorption unit is securely bolted to a substantial

foundationbutisabletoswivelclockwiseoranti-clockwisedependingontheforce

actinguponit.Thistendencytofollowtherotorrotationiscounteractedbymeans

ofa leverarmconnectedtoasensitive torquemeasuringapparatus.When the

statorswivels,theforceappliedtoitistransferredtothemeasuringapparatus.

Thestatorisforcedtofollowthemotionoftherotorbutisnotabletodoso.Asa

result,opposingforcesarecreatedwithinthedynamometer.Theforceappliedon

therotorisreferredasbrakingforceofthedynamometerandiscontrolledbythe

amountofcurrentflowingtroughthefieldcoil.



16

CHAPTER3–RECTIFICATION

Theactualdynamometerrectifierisobsoleteandusesvalverectifiertechnology.

To update the system with new power electronics, it is convenient for the

UniversityofSouthernQueensland tochangethevalve rectifierwithsolidstate

devices. This chapter includesanoverviewof rectifierusingsolidstatedevices

and demonstrates by means of experiment the basic principles for controlled

rectification.

3.1Thepowerdiodeorrectifierdiode3.1Thepowerdiodeorrectifierdiode3.1Thepowerdiodeorrectifierdiode3.1Thepowerdiodeorrectifierdiode

A diode is a two terminal device that allows an electric current to flow in one

direction but essentially blocks it in the opposite direction. The diode circuit

symbol is represented in figure 3.1. A semiconductor diode consists of a PN

junctionandthetwoterminalsarecalledtheanodeandthecathode.Currentflowsfrom anode to cathode within the diode as shown by the arrow of the circuit

symbol.

Figure3.1:DiodecircuitsymbolFigure3.1:DiodecircuitsymbolFigure3.1:DiodecircuitsymbolFigure3.1:Diodecircuitsymbol

Whenthevoltageacrossthediodeisnegativethediodeissaidtobereversed

biased and behaves as an open switch assuming ideal diode characteristics.

Whenthevoltageispositive,thediodeisforwardbiasedandworksasaclose

switch(Afhock2005).Figure3.2illustratestheidealoperatingcharacteristicsofa

practicalpowerdiode.



17

Figure3.2:IdealisedFigure3.2:IdealisedFigure3.2:IdealisedFigure3.2:Idealiseddiodecharacteristicdiodecharacteristicdiodecharacteristicdiodecharacteristic

3.23.23.23.2TheThyriTheThyriTheThyriTheThyristororSiliconCstororSiliconCstororSiliconCstororSiliconControlledontrolledontrolledontrolledRRRRectifierectifierectifierectifier(SCR)(SCR)(SCR)(SCR)

A thyristor is a semiconductor device thathas the same characteristicsas the

diode.Thyristorsareoftencalledsiliconcontrolledrectifiersandcompareto the

diodethethyristorisathreeterminaldevice.Themainterminalsofthethyristor

aretheanodeandthecathode.Thethirdterminalisreferredasagate.Figure3.3

illustratethethyristorcircuitsymbol.

Figure3.3:ThyristorcircuitsymbolFigure3.3:ThyristorcircuitsymbolFigure3.3:ThyristorcircuitsymbolFigure3.3:Thyristorcircuitsymbol

In the case that the thyristor is connected in serieswitha load through an AC

source, no current flows through the circuit until the thyristor as received a

triggeringsignalatthegateterminal.

Anode Cathode

Gate



18

Whenthepulseisreceivedittriggersthethyristorandallowscurrenttoflowfrom

anodetocathode.Figure3.4illustratethyristoridealisedcharacteristic.

Figure3.4:TypicalthyristorcharacteristicFigure3.4:TypicalthyristorcharacteristicFigure3.4:TypicalthyristorcharacteristicFigure3.4:Typicalthyristorcharacteristic

Once triggeredthethyristorcontinuestoallowcurrentto flow through thecircuit

duringthefirsthalfcycleofthesupply.Duringthenexthalfcyclethethyristordoes

notconductbecauseitisreversed-biased.

However,toconductafterbeentriggered,thecurrentthroughthethyristorhastobehigherthanthelatchingcurrentandlastforacertainperiodoftime.Toturnoff,

theanodecurrentisreducedbelowtheholdingcurrent.

Themostimportantcharacteristicofsiliconcontrolledrectifiersisthatconduction

can be delayed in each half cycle, to achieve a variable output voltage. The

triggeringpulsecausingtheconductionofthethyristortobedelayedisgenerated

bythefiringmodule.

Thisdelayofconductionisthedelaybetweentheinstantthethyristorwouldhave

conducted if it was a diode and the time that it is triggeredby the gate circuit

(Ahfock2005).



19

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

M e a s u r e m e n t

Time in millisecond

delay angle

AC source

Figure3.5illustratesthedelayofconductionalsocalledthedelayangle.

Figure3.5:HalfcontrolledhalfwaverectifierFigure3.5:HalfcontrolledhalfwaverectifierFigure3.5:HalfcontrolledhalfwaverectifierFigure3.5:Halfcontrolledhalfwaverectifier

• Thefiringmodule

Thefiringcircuitmustbedesignedsothatitwillonlygiveafiringpulseduringthe

time that the thyristor is forward biased. If the gate pulse is applied at the

beginningof thehalf-cycle,thecompletehalf-cyclewillbeappliedtothe load.If

thegatepulseisappliedanywhereelseduringthehalf-cycle,onlyaportionofthe

half-cycleisappliedtotheload.Itisthereforepossibletocontroltheloadvoltage

bycontrollingthegatepulseposition.

Thismethodofcontroliscalledlinearfiringanglecontrol.Tomakesurethateach

triggering pulses occur at a precise phase angle, the line supply voltage is

steppeddownthroughatransformerandthensenttothetriggeringmodule.As

thesignalhasbeensteppeddownitisstillinphasewiththemainssourcevoltage.



20

Asaresult,thegateterminalreceivesapulsegeneratedbythefiringmodulethat

willtriggerthesolidstateswitchataspecificdelayangle.

Figure3.6representstheblockdiagramofatriggeringmoduleandthewaveforms

obtainfor the triggeringprocess.Basically,asaw toothgeneratoroutputsa saw

toothwaveform(Vst)thatresetsatthezerocrossingsofthemainssupplyvoltage.

A controllable voltage (Vc) is generated by means of a potentiometer and

comparedtoVst.Sotheoutputofthevoltage comparator (Vp)willbelowifthe

controlvoltageisgreaterthanVstandviceversa.Finally,Vpisfedtoalogiccircuit

and converted a triggering pulse which is sent to the thyristor gate terminal.

(Afhock,2005).

Figure3.6:GatetriggercontrolcircuitandwaveformsFigure3.6:GatetriggercontrolcircuitandwaveformsFigure3.6:GatetriggercontrolcircuitandwaveformsFigure3.6:Gatetriggercontrolcircuitandwaveforms

(Wiley2003).



21

3.3Rectifiersconfigurations3.3Rectifiersconfigurations3.3Rectifiersconfigurations3.3Rectifiersconfigurations

Thecoilofthedynamometerrequiresdirectcurrenttogenerateasteadymagnetic

fieldforthebrakingprocesstooccur.Consequently,conversionofACtoDCmust

beachieved.

3.3.1Halfandfullwaverectification3.3.1Halfandfullwaverectification3.3.1Halfandfullwaverectification3.3.1Halfandfullwaverectification

TheprocessofconvertingACtoDCiscalledrectification.ThemajorityoftheDC

loads respond to themeanvalue ofaperiodicwave form. To obtain themean

valueofaperiodicsignal,theintegralofthesignalduringoneperiodisdividedby

theperiodinwhichitoccurs.Thewaveformobtainedfromthemainsissimilartoa

sinusoidalsignalrepresentedinfigure3.7.Whenusingthemeanvalueformulaon

asinusoidalsignal,theresultwillbezeroasthenetareaforoneperiodisequalto

zero.

Figure3.7:SinusoidalwaveformFigure3.7:SinusoidalwaveformFigure3.7:SinusoidalwaveformFigure3.7:Sinusoidalwaveform

Nevertheless,bymeansofsolidstatetechnologyitispossibletochangetheform

oftheinputsignalandobtainanapplicablemeanvalueofthesuppliedvoltagefor

thedevicetooperateinDCmode.Therearetwomainmanipulationsthatcanbe

achievedwhenrectifyingasinusoidalsignal.Thehalfwaverectificationorthefull

waverectification.

• Halfwaverectification

Theprocessof removing onehalfof the input signal toestablishaDC level is

calledhalfwaverectification.



22

InhalfwaverectificationthepositiveornegativehalfoftheACwaveispassed

easilywhile the other half is blocked, depending on the polarityof the rectifier.

Figure3.8demonstrateshalfwaverectificationofasinusoidalsignal.

Figure3.8:HalfwaverectificationFigure3.8:HalfwaverectificationFigure3.8:HalfwaverectificationFigure3.8:Halfwaverectification

The simplest formof rectifier circuit isa diode connected inserieswith the ac

input.Duringthepositivehalfcycleoftheinputvoltagethecurrentrepresentedin

figure3.9 flowsthroughtheloadresistor.Thediodeoffersavery lowresistance

and hence thevoltagedrop across it isvery small.Thus thevoltageappearing

acrosstheloadispracticallythesameastheinputvoltageateveryinstant.During

thenegativehalfcycleoftheinputvoltagethediodeisreversebiased.Practically

nocurrentflowsthroughthecircuitandalmostnovoltageisdevelopedacrossthe

resistor.

So, when the input voltage is going through its positive half cycle, the output

voltageisalmostthesameastheinputvoltageandduringthenegativehalfcycle

novoltageisavailableacrosstheload.Thisexplainstheunidirectionalpulsating

DCwaveformobtainedforhalfrectificationinfigure3.8.

Figure3.9:RectifiercircuitwithonediodeFigure3.9:RectifiercircuitwithonediodeFigure3.9:RectifiercircuitwithonediodeFigure3.9:Rectifiercircuitwithonediode

(Ahfock2005)



23

This rectifierconfigurationisclassifiedasuncontrolled rectification.Inhalfwave

rectificationtheACsourceonlyworkstosupplypowertotheloadonceeveryhalf-

cycle, meaning that much of its capacity is unused. However, half-wave

rectificationisthesimplewaytoreducepowertoaresistiveload.

TheAveragevoltageortheDCcontentofthevoltageacrosstheloadisgivenby:

[ ]

π π

π

ω π

ω ϖ ω π

π

π

π

π

peak peak avav

peak

av

peak

av

peak av

I R

V RV I

V V

t V

V

t d t d t V V

===

=

−=

+= ∫∫

.

cos2

)(.0)(sin.2

1

0

2

0

• Fullwaverectification

Figure3.10 illustrates full wave rectificationof thesame sinusoidal signal.The

negative or positive portions of the alternating signal are reversed and thus

produceanentirelypositiveornegativesignalwaveformdependingonhowthe

diodesareconnected.

Figure3.10:FullwaverectificationFigure3.10:FullwaverectificationFigure3.10:FullwaverectificationFigure3.10:Fullwaverectification



24

Forgreaterefficiency,itismoreconvenienttousebothhalvesoftheincomingAC

source.Arectifierthatconvertsbothhalf-cyclesofanACvoltagewaveformtoa

series of voltage pulses of the same polarity is called a full wave rectifier. To

obtainfullrectification,adifferentrectifiercircuitconfigurationmustbeused.Full

wave rectifier usesa four diode bridge connectionwhich is illustrated in figure

3.11.IftheACiscentre-tapped,thenthediodesarearrangedanode-to-anodeor

cathode-to-cathodetoformafull-waverectifier.

Figure3.11:DiodeBridgerectifierFigure3.11:DiodeBridgerectifierFigure3.11:DiodeBridgerectifierFigure3.11:DiodeBridgerectifier

Forthediodebridgecircuit,theinputsignalisasinusoidalvoltagesource.During

thefirsthalfcycle,thevoltageispositive.ConsequentlyatpointA thevoltageis

positiveandatpointBthevoltageisnegative.

TheAnodeofD1andD2ispositiveandthecathodeofD1andD4isnegative.

Duringthefirsthalfcycle,AispositiveandBisnegative,consequentlydiodeD1

andD2areforwardbiasedandcurrentflowsfromthesourcethroughD1,theload

andD2andbackintothesource.

Figure3.12:FlowofcurreFigure3.12:FlowofcurreFigure3.12:FlowofcurreFigure3.12:Flowofcurrentduringpositivecyclentduringpositivecyclentduringpositivecyclentduringpositivecycle



25

Duringthenexthalfcycle,thevoltageatpointAisnegativeandtheoneatpointB

ispositive.AsaresultD4andD3areforwardbiasedbecausetheiranodevoltage

ispositive and their cathode voltage is negative.During this periodof time the

currentwill flowaroundthecircuitasshown in figure3.13,again flowingin the

samedirectionthroughtheloadandproducinganotherpositivepulseofvoltage.

Figure3.13:FlowofcurrentduringnegativecycleFigure3.13:FlowofcurrentduringnegativecycleFigure3.13:FlowofcurrentduringnegativecycleFigure3.13:Flowofcurrentduringnegativecycle

The process of full wave rectification is illustrated in figure 3.10. Whenbridge

rectifiersuseonlydiodestheyaresaidtobeuncontrolled.Soas longastheAC

input does not vary it is not possible to adjust their D.C output. However,

combining diodes and thyristor within a bridge configuration leads to phase

controlledrectification.

TheAveragevoltageortheDCcontentofthevoltageacrosstheloadisgivenby:

[ ]

π

ω ω π

ω ω ω ω π

π

π

π

π

π

π

peak

av

peak

av

peak

av

V V

t t V

V

t d t t d t V

V

.2

]cos[cos2

)(sin)(sin2

2

0

2

0

=

−−−=

−= ∫∫



26

SCR1

D2D1

3.3.23.3.23.3.23.3.2HalfHalfHalfHalfandfullycontrolledrectifierandfullycontrolledrectifierandfullycontrolledrectifierandfullycontrolledrectifier

By using different combinations of diode and thyristor it is possible to obtain

different classes of rectifiers. Mainly because of the thyristor characteristic of

beingabletobephasedcontrolled,rectifieraresaidtobefullycontrolledwhen

usingfourthyristorswithinabridgeconfiguration.

The fully controlled bridge is usually used when it is necessary to regenerate

power form the load. The most widely used rectifier configuration is the half-

controlled bridge illustrated in figure 3.14. The main advantage of using half

controlledrectificationistoprovidetheloadanadjustableD.Coutputvoltagethat

varieswithrespecttothedelayangle.

For most of the applications using half controlled rectifiers, the control is only

possibleduringpositiveoutputvoltagefromthemains,andnocontrolispossible

whenthemainscyclesarenegative.

Figure3.14:Halfcontrolledbridgerectifier(SCRserie)Figure3.14:Halfcontrolledbridgerectifier(SCRserie)Figure3.14:Halfcontrolledbridgerectifier(SCRserie)Figure3.14:Halfcontrolledbridgerectifier(SCRserie)

3.4Testingonphasecontrolledrectifier3.4Testingonphasecontrolledrectifier3.4Testingonphasecontrolledrectifier3.4Testingonphasecontrolledrectifier

Aseriesoftestsonahalfcontrolledrectifierprovidedbytheengineeringfaculty

havebeenconductedinordertounderstandtheprocessofrectificationusingthis

configuration. In the following experiments two different rectifier configurations

havebeenused.

SCR2

Load



27

D1SCR1

SCR2

D2

Mostofthepowerelectronicapplicationsoperateatarelativehighvoltageandin

such cases the voltage drop across the SCR tends to be irrelevant for such

application.So,mostofthetime,theconductionvoltagedropacrossthedeviceis

assumedtobezeroforcircuitanalysis.Similarly,itisalsovalidtoassumethat

thecurrentthroughthethyristoriszerowhenitisnotconducting.

3.4.13.4.13.4.13.4.1ThehalfcontrolledbridgerectifierThehalfcontrolledbridgerectifierThehalfcontrolledbridgerectifierThehalfcontrolledbridgerectifier

There are two single phase half controlled rectifier configurations and both

operate in a same manner when connected to a resistive load. Figure 3.14

illustrate thyristors in series configuration and figure 3.15 shows the parallel

thyristors’configuration.

Figure3.15:Halfcontrolledbridgerectifier(SCRparallel)Figure3.15:Halfcontrolledbridgerectifier(SCRparallel)Figure3.15:Halfcontrolledbridgerectifier(SCRparallel)Figure3.15:Halfcontrolledbridgerectifier(SCRparallel)

Thedelayanglehasbeenfixedtoaparticularvalueandthecircuitisoperatingat

steadystate.DuringthefirsthalfcycleoftheACsource,thevoltageatpointAis

positive with respect to B.So, the load current flows only ifSCR2 is triggered.

SCR2 isthenturnedoffwhenthesourcevoltagebecomesnegative.Duringthis

cycle,BispositivewithrespecttoA,sothatSCR1andD2conducttheloadcurrent

when SCR1 is triggered. However,during the laps of time when SCR1 has not

beentriggered,theloadcurrentkeepsflowingiftheloadishighlyinductive.



28

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8RESISTIVE AND INDUCTIVE LOAD

M e a s u r e m e n t s

Time in millisecond

Main voltage

Load current

Rectified voltage

Thisinductivecurrenthastwocircuitswhereitcanflow,onemadebytheSCR2,

the source andD1 andasecond,made by SCR1andD1. Because of the low

impedanceofthesecondcircuit,thecurrentcontinuetoflowthroughSCR 1andD1

whilethevoltageisnegative.

Thebacke.m.f fromtheinductive loaddrivescurrent through thebridgewithout

containing any of the reverse supplyvoltage.During this time interval the load

current decays exponentially. Thyristor SCR1 is then triggered in the next half

cycleandthecyclerepeats.Figure3.16illustratestheoutputofahalfcontrolled

bridgerectifierconnectedtoaninductiveload.

Figure3.16:HalfcontrolledbridgerectifieroutputFigure3.16:HalfcontrolledbridgerectifieroutputFigure3.16:HalfcontrolledbridgerectifieroutputFigure3.16:Halfcontrolledbridgerectifieroutput



29

Thishalfcontrol rectifierconfiguration isgoodwhentheloadisnottooinductive

andwith a time constant much lower than one half cycle of the supply. On a

contrary,iftheloadishighlyinductivewithatimeconstantgreaterthanonehalf-

cycleofthesupply,itwillbecomemoredifficulttoturnofftheloadcurrentjustby

notsendinganypulsetothegate.

If the triggerpulses are removed after that a thyristor has been triggered, this

thyristor will continue to conduct as usual for the rest of the half cycle of the

supply.Then,theotherthyristorwillnotturnonbecausenotriggeringpulsewillbe

senttoassureconduction.Thecircuitwillcontinuetooperateindefinitelywiththe

firsttriggeredthyristorconductingoncompletealternatehalfcycleandactingasa

flywheeldiodeontheotherhalfcycles.Inthiscase,theonlywaytointerruptthis

cycle will be to stop the mains supply.Nevertheless, to ensure that the circuit

operatessatisfactorilyafreewheelingdiodecanbeaddedinparalleltotheload.

Consequently, at the end of each half cycle of the supply the load current is

transferreddirectlytothisdiode.Thefreewheelingdiodeensuresthatthereisno

riskthatathyristorwillcontinuetoconductoveranotherhalfcycle.(ed.Mullard

1970).

Theaverageoutputvoltageofthebridgeasafunctionoffiringangle:

[ ]

]cos1[

]cos[cos

cos

)(sin

α π

α π π

ω π

ω ω π

π

α

π

α

+=

−−

=

−

=

= ∫

peak

av

peak

av

peak

av

peak

av

V V

V V

t

V

V

t d t V

V



30

TheRMSloadcurrentduringα<wt<π:

][)sin()(

)(tan

1

][)sin()(

1

2

τ

α π

τ

α ϖ

β π π

τ β

ω τ

τ

β ω ω

−−

−

−

−

×+−×=

=

=

+×=

×+−×=

e A Z

V i

and

R

L

R Z

where

e At Z

V t i

peak

load

t peak

load

TheRMSloadcurrentduringπ<wt<π+α:

][)()(τ

π ϖ

π ω

−−

+=

t

load load it i

Whentheloadcurrentisrepetitive

τ

π

τ

π

τ

α

β α β π

β π α π

β α α

π α α

−

−−

−

−−−×=

+×−×=+

+−×=

+=

e Z

V A

e Ae Z

V i

A Z

V i

ii

peak

peak

load

peak

load

load load

1

)sin()][sin(

)sin()(

)sin()(

)()(



31

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8RESISTIVE AND INDUCTIVE LOAD

M e a s

u r e m e n t s

Time in millisecond

OnceAisknown,thetotalRMSvalueoflinecurrentandtheRMSvalueofits

fundamentalcomponentcanbeestimated.

3.4.2Fullycontrolledhalfwaverectifierwithafreewheelingdiode3.4.2Fullycontrolledhalfwaverectifierwithafreewheelingdiode3.4.2Fullycontrolledhalfwaverectifierwithafreewheelingdiode3.4.2Fullycontrolledhalfwaverectifierwithafreewheelingdiode

Theoperationofthisrectifierconfigurationisverysimilartothesinglediodecircuit

represented in figure 3.9. The only difference is that this configuration uses a

thyristorconnectedinserieswiththeloadandadiodeconnectedinparallel.

Figure3.17:fullycontrolledhalfwaverectifieroutputFigure3.17:fullycontrolledhalfwaverectifieroutputFigure3.17:fullycontrolledhalfwaverectifieroutputFigure3.17:fullycontrolledhalfwaverectifieroutput

Inthefirstpositivehalfcycle,thethyristorisforward-biasedhoweveritwillonly

conductifthedevicewillreceivethefiringpulse.Ifitisnottriggered,nocurrent

willbedeliveredtotheload.



32

Asexplainedearlier, when the thyristor is triggered in the forward-bias state, it

startsconductingandthepositivesourcekeepsthedeviceinconductionuntilthe

sourcevoltagebecomesnegative.Atthatinstant,thecurrentthroughthecircuitis

notzerobecausethereissomeenergythathasbeenstoredintheinductor.

Theinductordischargesthisenergyduringthenegativecycleofthemainssource

throughthefreewheelingdiode.So,whenthefreewheelingdiodeconducts,the

thyristor remains reverse-biased,becausethesourcevoltage isnegative.In the

absence of the free wheeling diode, the inductor would keep the thyristor in

conductionduringthenegativecycleofthesourcevoltageuntiltheloadisfully

discharged.



33

CHAPTER4–TESTANDDESIGN

The updated half wave rectifier has to be tested on the dynamometer.

Subsequently, testswillbe implemented inorder to localisewhere theupgraded

rectifierwillbeconnected.

4.1Inputandoutputlocation4.1Inputandoutputlocation4.1Inputandoutputlocation4.1Inputandoutputlocation

Originally,theprotectivecircuitoftheinitialcircuitwassupposedtobereusedwith

the upgraded rectifier circuit. However, this task was requiring meticulous

investigationsandthusmoretime.Therefore,itwasmoreconvenienttore-design

thewholeunitcontrolandkeepthevalvecircuitintact.Asaresult,theentirevalve

systemwasdisconnectedsothatiftheupgradedsystemfailstooperate,theinitial

electronic unit will still be able to operate the plant. The first approach was to

determinetheinputandoutputconnectionsofthecircuit.

Figure4.1:ExternalwiringconnectionofthedynamometerFigure4.1:ExternalwiringconnectionofthedynamometerFigure4.1:ExternalwiringconnectionofthedynamometerFigure4.1:Externalwiringconnectionofthedynamometer




34

Figure 4.1 illustrates the connections between the dynamometer bed plate

connector block and the electronic input panel. As depicted, none of the

dynamometerbedplateconnectionsarewelldefined.However,itcanbeseenthat

the dynamometer is connected to the electronic circuit via six input or output

connections.

Thedynamometermustbeprotectedagainstoverheating. Inthecoolingsystem

located on the dynamometer side, is embedded a water pressure switch which

sensesthewaterpressure.Ifthewaterpressureisnotsufficienttheswitchopensa

protective circuit which shuts down the engine coupled to the dynamometer.

Consequently,theremustbeasignalfromthedynamometertoindicatelowwater

pressurelevel.

Similarly, the dynamometer has to be protected against over speeding. As

explainedinthehandbook, ifthedynamometerspeedrisesaboveapresetvalue

thesystemwillalsoshutsdownautomatically.Consequently,anoutputsignalfrom

thetachogeneratorwhichislocatedonthedynamometersidemustbefedtothe

controlunittodetectwhentheenginespeedgoesaboveaspeedlimit.

Finally, the dynamometer field coil has to be roused to generate the primary

magneticfieldforbrakingprocesstooccur.So,theremustbeaninputsignalfrom

thecircuitthatregulatestheamountofcurrentgoingthroughthecoil.

4.2Preliminarytests4.2Preliminarytests4.2Preliminarytests4.2Preliminarytests

Thedynamometerbedplateconnectorblockcontainsfouroutputsandoneinput

connectiondescribeasC1,C2,A2,A1,W2,W1.



35

The information contained within the handbook does not define any of these

connections;subsequentlyassumptionsweremadebeforeimplementingtestson

thedynamometer.

Atfirst,connectionC1andC2wereassumedtorefertothecoilconnectionand

thereforeenablesasignaltogofromtheelectroniccircuittothefieldcoil.Then,it

was assumed that connection W1andW2wereassumed to refer to the water

pressure switch locatedwithin thedynamometer.And finally, connectionA1and

A2wereassumedtobetheanaloguesignalgeneratedby thetachogeneratorto

preventtheenginetooverspeed.

ConnectionIG.1,IG.2,andIG.3aredefinedastheengineignitionconnectionand

areusedtosafeguardtheengineincaseofoverspending,orfailureofwateror

electricitysupplies.ThemainpowersupplyisdefinedbytheLandNconnections

tooperatethewholesystem.

ToverifytheassumptionsaboutconnectionsC1,C2,A2,A1,W2,W1,aseriesof

testswereimplementedonthedynamometerbedplateconnections.

• TestatterminalsC1andC2

The inputsignaloftheexcitedcoilmustbearectifiedversionof themainsource

voltage.ThebestapproachtoensurethatC1andC2arethedynamometercoil

input connections a digital oscilloscopewas connected across them. Figure4.2

illustratesthesignalobtainacrosstheseconnections.

As depicted, the signal ishalf rectified and thereforemustbe the output of the

valve rectifier.As a result, C1 and C2 are defined tobe the dynamometer coil

connection.



36

- 0.02 5 -0.02 -0 .01 5 -0.0 1 -0 .005 0 0 .005 0.01 0. 015 0.02 0. 025-0.1

0

0 .1

0 .2

0 .3

0 .4

0 .5

0 .6

0 .7Output from c onnection C1 and C2

r e c t i f i e d V o l t a g e w a v e f o r m

Time in millisecond

Figure4.2:SignalobtaFigure4.2:SignalobtaFigure4.2:SignalobtaFigure4.2:SignalobtainedacrossconnectionC1andC2inedacrossconnectionC1andC2inedacrossconnectionC1andC2inedacrossconnectionC1andC2

• TestatterminalsW1andW2

As explained before,W1andW2are assumed tobe thewater pressureswitch

connection of the protective circuit. Consequently, these connections must be

connectedatbothendsoftheswitchrepresentedinfigure5.1.

Aperfectswitch,bydefinition,willhave0Ωwhenclosedanditwillhaveinfinite

resistancewhenopened.Tochecktheresistancebetweenthesetwoconnections,

anammeterwasconnectedacrossthem.

Theresultobtaineddemonstratedthatwhenthereisnotwaterflowingwithinthe

coolingsystem,theresistanceacrossW1andW2isinfinite.Onthecontrary,when

thewatertapeisopen,theresistanceisapproximatelyequalto0.3.Thistest

hasproventhatconnectionW1andW2arethewaterpressureswitchconnection.



37

- 3 -2 - 1 0 1 2 3

x 10-3

-0.1

- 0 . 0 8

- 0 . 0 6

- 0 . 0 4

- 0 . 0 2

0

0 . 0 2

0 . 0 4

0 . 0 6

0 . 0 8

0 .1Ou tp u t f r o m c o n n e c t i o n A 1 a n d A 2

T a c h o m e t e r o

u t p u t v o l t a g e

T ime in m i lli seco n d

• TestatterminalsA1andA2

The system uses an analogue tachometermountedon the dynamometer shaft.

Thedevicegeneratesanoutputvoltagethatisproportionaltotherotationalspeed.

To provethatA1 andA2are the tachometer outputs, adigital oscilloscopewas

connectedacrosstheseconnectionswhilethesystemwasrunning.Asassumed,

whenthespeedwasincreasedordecreasedthesignalamplitudeandfrequencies

werechangingwithrespecttotheenginespeed.Figure4.3showstheoutputofthe

tachogeneratoratacertainspeed.

Figure4.3:Figure4.3:Figure4.3:Figure4.3:SignalobtainSignalobtainSignalobtainSignalobtainacrossacrossacrossacrossconnectionconnectionconnectionconnectionAAAA1and1and1and1andAAAA2222

Toconfirmthatthevoltagewaschangingwithrespecttospeed,theproportionality

betweenspeedandamplitudewasalsochecked.Whenthesystemwasrunning,

thevoltageRMSandspeedreadingwereproceedandstoredintable4.1.



38

Tachometer linearity

speed vs voltage

0

500

1000

1500

2000

2500

3000

3500

20.9 29.6 38.9 49.6 58.8

Voltage rms

s p e e d r p m

Table4.1:TachogeneratoroutputvoltageatacertainspeedTable4.1:TachogeneratoroutputvoltageatacertainspeedTable4.1:TachogeneratoroutputvoltageatacertainspeedTable4.1:Tachogeneratoroutputvoltageatacertainspeed

Thefollowingfigureillustratestheproportionalrelationshipbetweenspeedandthe

voltage.

Figure4.4:LinearitybetweentheoutputvoltageandspeedFigure4.4:LinearitybetweentheoutputvoltageandspeedFigure4.4:LinearitybetweentheoutputvoltageandspeedFigure4.4:Linearitybetweentheoutputvoltageandspeed

SpeedRPM VOLTAGERMS

1000 20.9

1500 29.6

2000 38.9

2500 49.6

3000 58.8

3500 62.3



39

CHAPTER5–PROTECTIVESYSTEM

Protectionoftheplantwhileitisoperatingisessential.Thewholeplanthastobe

protectedagainstoverspeedingandoverheating.Atthesametime,theusermust

besafeandhastobeprotectedagainstanyindependentemergency.Thischapter

explainstheuseofaprotectivecircuitandbrieflydescribestheprotectivesystem

usedwiththevalverectifier.Followingthat,itgivesadescriptionoftheselected

devicesusedforprotection.

5.1Theexistingprotectionsystem5.1Theexistingprotectionsystem5.1Theexistingprotectionsystem5.1Theexistingprotectionsystem

The circuit depicted in figure 5.1 represents the actual protective circuit that

safeguards the engineand the dynamometer in the eventof water failure, over

speedingorfailureofthepowersupply.

Figure5.1:ExistingprotectivecircuitFigure5.1:ExistingprotectivecircuitFigure5.1:ExistingprotectivecircuitFigure5.1:Existingprotectivecircuit




40

5.1.1Thewaterpressurea5.1.1Thewaterpressurea5.1.1Thewaterpressurea5.1.1Thewaterpressureandignitionswitchesndignitionswitchesndignitionswitchesndignitionswitches

• Thewaterpressureswitch

Cooling thedynamometer innerrings isessential tosafeguardthedynamometer

because considerabledamagewouldbedone if the instrumentoverheated.The

heatgeneratedbytheinducedcurrentwouldmeltthestatorinnerringsiftheyare

notcooledproperly.

As explained in the dynamometer handbook, each brake power absorbed

generates 42.4 B.Th.U per minute, nearly all of which passes into the cooling

water. Consequently, the water pressure must be sufficient to ensure the

temperatureofthestatorinnerringsdoesnotriseabove140degreesCelsius.

Tosensethewaterpressureinthecoolingsystem,aspecificprotectivedeviceis

used.Itisreferredintothehandbookasthewaterpressureswitch.Theswitchis

embedded within the dynamometer cooling system and is connected to the

electronicunitbymeansoftheconnectionsW1andW2.Whenwaterisrunning

throughthedynamometerwithenoughpressure,thewaterpressureswitchcloses

aprotectivecircuitsothatthesystemissafetorun.Onthecontrary,ifthewater

pressure isnotsufficient tocool the inner rings, theswitchopens theprotective

circuitsothatthesystemisshutdownorcannotstart.

• Theignitionswitch

This ignition switch is amanually-operated switch and has tobe closed for the

combustion engine to start. The main purpose of this switch, however, is to

safeguardthesystemortheuserintheeventofanindependentemergency.



41

5.1.2Theconnectionsofthecoilignitionengin5.1.2Theconnectionsofthecoilignitionengin5.1.2Theconnectionsofthecoilignitionengin5.1.2Theconnectionsofthecoilignitionengineeee

IG.1, IG.2 and IG.3 are the three terminals from the electronic input panel

connectedwith theengine ignitionsystem. The LowTension connections of the

coilignitionengineareconnectedinserieswithterminalIG.1,IG.2andIG.3.These

terminals are connected to the second ‘change-over contact’ of a double pole

doublethrowrelayasdepictedinfigure5.2.

Tostoptheenginewhenafaultoccurs,thechangeovercontacthastobeonIG.1

andIG.2.Fortheenginetostart,IG.2andIG.3mustbeconnected.TheDouble

PoleChangeOver(D.P.C.O)relayhastworowsofchange-overterminalsand is

actuatedbyasinglecoil.

Figure5.2:DoublePoleDoubleThrowrelay(DPDT)Figure5.2:DoublePoleDoubleThrowrelay(DPDT)Figure5.2:DoublePoleDoubleThrowrelay(DPDT)Figure5.2:DoublePoleDoubleThrowrelay(DPDT)

(Handbook,1881)

5.1.3ResettingtheDPCOrelay5.1.3ResettingtheDPCOrelay5.1.3ResettingtheDPCOrelay5.1.3ResettingtheDPCOrelay

To reset the relay, a momentary push button switch is connected to the first

change-over contactof therelay.Referring to figure5.1, if thewater switch, the

ignition switch and the RL1 internal switch are closed, then by pressing and

depressing the reset button the relay becomesenergized,so that contacts IG.2

becomesconnectedtoIG.3.



42

As a result, the engine is ready to be started and thewhole system is safe to

operate. For the engine to start, the entire set of switches that constitute the

protectionsystemhavetobeclosed.Ifanyoftheswitchesopenwhilethesystem

operatestheengineisturnedoffautomatically.Forexample,ifthewaterpressure

is insufficient, thewater pressureswitchwill open.Consequently, thecoil of the

relaywillbede-energizedandtherelaywillreturntoitsinitialstatewhereIG.2is

connectedtoIG.1.

5.1.3Overspeedcontrol5.1.3Overspeedcontrol5.1.3Overspeedcontrol5.1.3Overspeedcontrol

ThefunctionofthefirstrelayRL1,representedinfigure5.2,istostoptheprime

mover if the loadgenerated by the dynamometer fails.When the load fails it is

commonlyduetoeithera failureofthemainsupplyora faultoccurringwithinthe

excitationunit.Ifasuddenfailureoftheloadoccurs,thespeedoftheenginewill

risesoquicklythatconsiderabledamageswouldoccurtotheprimemover.

Infigure5.1,valveV8isbiasedoffbyadjustingthepotentiometerP3.Theposition

ofP3determinesthespeedatwhichtheplantshouldshutdown .V8willremain

biased off until the rectified signal from the tacho generator exceeds the bias

condition.InthecasethattherectifiedD.Csignalexceedstheoverspeedcutout

adjustorlimit,V8willallowcurrenttopassandwillenergisedthecoilofRL1.Asa

result, Relay one open the protective circuit and de-energises Relay two (RL2)

whichclosescontactsIG.1andIG2(Dynamometerhandbook).

5.2Upgradedprotectionsystem5.2Upgradedprotectionsystem5.2Upgradedprotectionsystem5.2Upgradedprotectionsystem

Anupgradedversionoftheinitialprotectivesystemhasbeendesignedandtested

onto the dynamometer. The circuit uses the latest technology available from

Farnell’scatalogue2005.



43

The circuit guarantees that the engine stops automatically in the event of

insufficientwaterpressure,overspeedingorafaultoccurringintheexcitationunit.

For design simplicity and convenience, thewater pressuresensor has been re-

used.

5.2.25.2.25.2.25.2.2OverspeedingprotectiondeviceOverspeedingprotectiondeviceOverspeedingprotectiondeviceOverspeedingprotectiondevice

Asexplainedearlier,thecircuitmustpreventoverspeedingforengineprotection.

Whenthespeedofthedynamometershaftrisesaboveapresetvalue, theprime

movermuststop.ThemostsuitabledeviceforthisoperationistheMultifunction

Voltage Relay also called the M3MVR. As a result, the section of the initial

protectivecircuitrepresentedinfigure5.3isreplacedbyusingonlythisdevice.

Figure5.3:OverspeedprotectionusedwithinitialdesignFigure5.3:OverspeedprotectionusedwithinitialdesignFigure5.3:OverspeedprotectionusedwithinitialdesignFigure5.3:Overspeedprotectionusedwithinitialdesign


TheM3MVRautomaticallyadjustsforACorDCsupply.Therelaycanbeusedfor

eitherundervoltagemonitoringorovervoltagemonitoring.Forthisapplicationthe

deviceisusedforovervoltagemonitoring.Thetrippingmodeoftherelaymustbe

selectedatthetimeofinstallationbymeansofarearmountedswitch.Figure5.4

illustratestheM3MVRrelay.



44

Figure5.Figure5.Figure5.Figure5.4444::::M3MVRandfrontpanelM3MVRandfrontpanelM3MVRandfrontpanelM3MVRandfrontpanel

(Source:http://www.broycecontrol.com)

For this application, the M3MVR is used to track if the voltage output from the

tachogeneratorgoesaboveapresetvoltage.AssoonastheM3MVRreceivesan

analoguesignalwithapeakvalueabovethelimit,theinternalswitchopensand

thusopenstheprotectivecircuit,stoppingtheengine.

Whenthe relayhastriggered itcanberesetbyeithermomentarilyremovingthe

powersupplyorturningthelatchswitchtotheoffposition.

Themainadvantageofferedbythisrelayisthatifaspikeisgeneratedbythetacho

generatortherelaywillnotrespondtothishighvoltage.Inorderfortherelaytotrip,

the analogue signal should stay above the preset over voltage limit for a pre-

definedintervaloftime.Thetime(t),infigure5.5representsthetrippingtimedelay.

The relaycan be set todelay tripping, for 100ms or 1 second,using the front

mounteddelayswitch.



45

Figure5.5:TimingdiagramforovervoltagemonitoringFigure5.5:TimingdiagramforovervoltagemonitoringFigure5.5:TimingdiagramforovervoltagemonitoringFigure5.5:Timingdiagramforovervoltagemonitoring

(Source:http://www.broycecontrol.com)

Iftherelayismonitoringclosetoitstrippingpoint,itmightcontinuouslypullinand

dropoutasthevoltagecontinuallypassesthroughthesetpoint.Toovercomethis

problem, anadjustablehysteresis levelhas been incorporated to therelay.This

causestherelaytore-energiseatapointwhichisateither2%or10%belowthe

setpointlevel.Thechoiceofhysteresislevelcanbemadeusingthefrontmounted

switch (see figure 5.4). TheM3MVR is able to monitor two different ranges of

voltages.

M3MVRtechnicalspecifications:

Supplyvoltage(nominal):18–240VAC50/60Hz

Min./maxlimits:15–265VAC48/63Hz

Powerconsumption:3VA

Outputcontactratings:8A,250VAC

Inputimpedance:10MΩ

Monitoringranges:

Range1 1to26.5VAC

Range2 10to265VAC

Maximuminputvoltage:1000V



46

Figure5.6representsthesectionoftheupgradedprotectioncircuitthatwillprotect

theengineagainstoverspeeding.

Figure5.6:M3MVRFigure5.6:M3MVRFigure5.6:M3MVRFigure5.6:M3MVR

5.2.3Resettingtheinitialstateofthecircuit5.2.3Resettingtheinitialstateofthecircuit5.2.3Resettingtheinitialstateofthecircuit5.2.3Resettingtheinitialstateofthecircuit

The most suitable relay to control the state of the engine and thus guarantee

protection of thewhole system is the DPCO-5532, illustrated in figure 5.7. This

miniaturegeneral purpose relay is calledan "ice cube" relay in reference to its

transparent enclosure and size. The transparency allows inspection of the

contacts,coil,andswingarmsforevidenceofoverheating.

Figure5.7:DPCOFigure5.7:DPCOFigure5.7:DPCOFigure5.7:DPCO----5532553255325532

Contactsspecifications:

Contactconfiguration:2Changeover,DPDT.

Ratedcurrent/Maximumpeakcurrent:10A.

Ratedvoltage/Maximumswitchingvoltage:250VAC.

Tacho

M3MVR



47

DPCO

Coilspecification:

Voltage,coilACnominal:230V.Coilresistance:17Ω.

This relay is the core of the protection system. When its coil is energised, it

maintainscircuitprotection,andwhenthecoilisde-energisedtherelayshutsdown

theenginebymeansofIG.1,IG.2andIG.3.

5.2.4Protectivecircuitconfiguration5.2.4Protectivecircuitconfiguration5.2.4Protectivecircuitconfiguration5.2.4Protectivecircuitconfiguration

Whiledesigningthenewprotectivecircuit,itwasmoreconvenienttorefermostof

thedesignto theoldcircuit.Theupgradedprotectivesystemisdepictedin figure

5.8. Thewater switchcloses as soonas there is enough water pressure in the

coolingsystem.Whentheignitionswitchismanuallyclosed,thesystemisready

to operate and an indicator indicates that the plant is ready. However, before

startingtheenginetheresetbuttonhastobepressedanddepressedsothatthe

relay“DPCO–5532”becomesenergizedandclosescontactsIG.2andIG.3.

Figure5.8:ProtectivecircuitFigure5.8:ProtectivecircuitFigure5.8:ProtectivecircuitFigure5.8:Protectivecircuit

Tacho

M3MVR



48

CHAPTER6–THEUPGRADEDSYSTEM

Upgradingtherectifyingsystemhasrequiredaselectionofspecificdevices.This

chapter introduces theselected devicesused for rectification and describes the

operationoftheupgradedsystem.

6666.1.1.1.1ThehalfcontrolbridgerectifierThehalfcontrolbridgerectifierThehalfcontrolbridgerectifierThehalfcontrolbridgerectifier

6.1.16.1.16.1.16.1.1ACtoDCconverterACtoDCconverterACtoDCconverterACtoDCconverter

Siliconcontrolledrectifiersareavailableinavarietyofintegratedcircuitpackages

which have different number of pins. After a meticulous search for the most

suitabledevice,theintegratedpowercircuitsP102Wwasselectedtoconvert the

AC source to DC. This device consists of power thyristors and power diodes

configured in a single package as illustrated in figure 6.1. As depicted in the

following figure, the module is mounted on an alumina substrate to provide a

completelyisolatedassembly.

Figure6.1:P102WFigure6.1:P102WFigure6.1:P102WFigure6.1:P102Wmodulemodulemodulemodule

(Source:http://www.farnell.com)



49

Figure6.2 illustrates the internal configurationof themodule and shows that the

modulehasafreewheelingdiodeconnectedinparalleltotheloadofthemodule.

Figure6.2:Figure6.2:Figure6.2:Figure6.2:IIIInternalbridgerectifierconfigurationnternalbridgerectifierconfigurationnternalbridgerectifierconfigurationnternalbridgerectifierconfiguration

(Source:http://www.irf.com)

Table6.1detailsallthemajorratingsandcharacteristicsoftheP102Wmodule.

Table6.1Table6.1Table6.1Table6.1:P102Wratingsandcharacteristics:P102Wratingsandcharacteristics:P102Wratingsandcharacteristics:P102Wratingsandcharacteristics

(Source:http://www.irf.com)



50

• Heatsink

Whentheinternaldiodesorthyristorsareforwardbiased,thereisacurrentflowing

through it, as well as a voltage across it. Semi conductor power losses are

dissipatedintheformofheat,whichmustbetransferredawayfromtheswitching

junction (William1992). An excessive amount of heat can be damaging or

destructivetothemodule.Inordertocontrolthemoduletemperature,thedeviceis

mountedonaspecificheatsinkwhichensuresagoodthermalequilibriumbetween

thejunctiontemperatureandtheambienttemperature.Thefollowingtabledetails

thethermalandmechanicalspecificationoftherectifiermodule.

TableTableTableTable6.6.6.6.2:ThermalandmechanicalspecificationoftheP102Wmodule.2:ThermalandmechanicalspecificationoftheP102Wmodule.2:ThermalandmechanicalspecificationoftheP102Wmodule.2:ThermalandmechanicalspecificationoftheP102Wmodule.

(Source:http://www.irf.com,2006)

Thethermalresistanceoftheheatsinkdependsonitssize,itsconstructionandits

orientation. Figure 6.3 illustrates the heat sink where the rectifying module is

mounted.



51

FFFFigure6igure6igure6igure6.3.3.3.3:Heatsink:Heatsink:Heatsink:Heatsink

Theheatssinkhasathermalresistanceof0.85°C/Wandismadeofaluminium.It

utilisefinnedsurfaceareaonbothsideofthemodulemountingsurfaceinorderto

providemaximumheatdissipation.

6.1.26.1.26.1.26.1.2FiringmoduleforFiringmoduleforFiringmoduleforFiringmodulefortheP102WtheP102WtheP102WtheP102W

The selected triggermodule illustrated in figure 6.4 uses variable phase angle

controlwithadjustablesignalmatching,integralcurrentlimitinputandadjustable

softstart.

Figure6.Figure6.Figure6.Figure6.4444:AFM:AFM:AFM:AFM----11111111

(Source:http://www.powercontrollers.net/components/firing_circuit)



52

Asdepictedinfigure6.5,themoduleoffersfourdifferentwaystocontrolthephase

anglegeneratedbythefiringmodule.Controlcanbeachievedviaaninputsignal,

a relay, a manual potentiometer or a DC input signal. The module offers an

adjustable current limit option that can be used when designing the close loop

system.

Figure6.Figure6.Figure6.Figure6.5555:Controloptionforterminal5,4and3:Controloptionforterminal5,4and3:Controloptionforterminal5,4and3:Controloptionforterminal5,4and3

(Farnell,2005)

• Thecontrolpotentiometer

Although,therearedifferentmethodsavailabletocontroltheangleofconduction,

theuseofamanualpotentiometerisoneofthemostsuitableoptionstomanually

controltheloadgeneratedbythedynamometer.A5kΩpotentiometerillustratedin

figure6.6isconnectedtothefiringmodule.

Figure6.Figure6.Figure6.Figure6.6666::::5k5k5k5kΩΩΩΩpotentiometerpotentiometerpotentiometerpotentiometer

(Source:http://www.farnellinone.com)



53

• Supplystepdowntransformer

Inorder tooperate the triggeringmodule and themultifunction relay, themains

sourcehastobestepdownto24VAC.Thetransformerillustratedinfigure6.4isa

stepdowntransformerthatconverts230VACto24VAC.Asillustratedinpicture

6.7thetransformerprovidestwosecondaryvoltages.

Figure6.Figure6.Figure6.Figure6.7777:Transformer:Transformer:Transformer:Transformer

(Source:http://www.farnellinone.com)

Transformercharacteristics:

Power,AC:12VA

Voltages,secondary:0-24,0-24

Voltage,singleprimary:230V

Power,persecondarywinding:6VA

Regulation:12%

(AppendixEdetailsthecostofthesedevices)

6666.2.2.2.2UpgradedUpgradedUpgradedUpgradedsystem:system:system:system:ManualtorquecontrolManualtorquecontrolManualtorquecontrolManualtorquecontrol

Asexplainedearlier, thenewcontrolunitmustsupplythedynamometer fieldcoil

withanadjustableDCsource.However,thewholesystemhastobeprotectedand

safetouse.



54

Theupgradedsystemconsistsoftheprotectioncircuitandtheupgradedrectifier.

Figure6.8illustratestheblockdiagramrepresentationoftheupgradedsystem.

Figure6.Figure6.Figure6.Figure6.8888:Upgra:Upgra:Upgra:Upgradeddeddeddedcontrolunitcontrolunitcontrolunitcontrolunitsystemsystemsystemsystem

The control potentiometer is connected directly to the firing module to ensure

manual loadcontrol.Oncethepotentiometerissettoacertainposition,thefiring

module generates a pulse signal which occurs at a specific delay angle. As a

result,theP102Wproducesaconstantlevelofdirectcurrenttothefieldcoiland

thus generate a load that will quickly become constant irrespective of further

enginespeedrise.

ThenewcontrolunitisconnectedtotheelectronicinputpanelillustratedinFigure

6.9Theseconnectionsarelocatedwithintheinitialcontroldesk.



55

Figure6.Figure6.Figure6.Figure6.9999:E:E:E:Electronicinputpanellectronicinputpanellectronicinputpanellectronicinputpanel

6.3Laboratorytestingontheupgradedsystem6.3Laboratorytestingontheupgradedsystem6.3Laboratorytestingontheupgradedsystem6.3Laboratorytestingontheupgradedsystem

Beforeimplementinganytestingontothedynamometer,thenewcircuitwastested

inlaboratorytoverifyifthecircuitwasworkingproperly.Figure6.10illustratesthe

testingconfigurationoftheupgradedsystem.

Figure6.Figure6.Figure6.Figure6.10:Tes10:Tes10:Tes10:Testingconfigurationoftheupgradedsystemtingconfigurationoftheupgradedsystemtingconfigurationoftheupgradedsystemtingconfigurationoftheupgradedsystem

Variac

1:1Transfo

6AfuseOscilloscope

Upgraded

circuit

Load



56

-0.025 -0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025-400

-300

-200

-100

0

100

200

300

400RESISTIVE AND INDUCTIVE LOAD

M e a s u r e m e n t s

Time in millisecond

Thefirsttestwasperformedtoverifyif rectificationwasoccurring.To replacethe

dynamometercoil,aninductiveloadwasconnectedinserieswitharesistiveload.

Theoutputwaveformofthesourcevoltageandtherectifiedsignalwasobtained

viaadigitaloscilloscope(TektronixTDS420A).Figure6.11illustratestherectifier

outputataspecificangleofconduction.

Figure6.11Figure6.11Figure6.11Figure6.11::::UpgradedUpgradedUpgradedUpgradedrectifieroutputrectifieroutputrectifieroutputrectifieroutput

The second series of tests was organised to check the reset condition of the

protective circuit and if the system shuts down in the event of over speeding.

Figure6.12illustratethecircuitconfigurationtestedwithinthelaboratory.

Theresetconditionof theprotectivecircuithasbeenverifiedbyensuring thatno

voltage was across theDPCO coil before the reset button was pressed. Thus,

whentheresetbuttonwaspressedanddepressed,230VACappearedthrough

thesamecoilandaredlamplightstoindicatethattheplantisready.Thereset

option works as expected so further testings were carried out to verify over

speedingprotection.



57

The reset button has been pressed and depressed so that the system is now

protected. If the internal switch of theM3MVRopens, themagnetic field of the

DPCO coil collapses and thus connection IG.2connects to IG.1in order to shut

downtheengine.

Toensurefullsystemprotectionagainstoverspeedingwithinthelaboratory,the

mainACsourcewasconnectedtoavariactoobtainvariableACsourcethatwill

replace the tacho generator output in the laboratory.The signal from the variac

wasfedtothemonitoredinputconnectionoftheM3MVRrelaywiththeintentionof

trackingifthevoltagegoesaboveapredefinedvalue.Whenthemonitoredsignal

goesabovethevoltage limit,the internalswitchof the relayopenstheprotective

circuit,sothattheDPCOrelayswitchesbacktoitsinitialstateandthusstopthe

engine.

ToguaranteethattheDPCOhadswitchedbacktoitsinitialstate,theresistance

acrossthesecondinternalswitchoftheDPCOrelaywasmeasuredviaanampere

meter.Whenthewholesystemisprotected,theresistanceacrossIG2andIG1is

veryhigh.On the other hand,when the system isnotprotectedorwhen a fault

occurs,theresistanceacrosstheseterminalsisverylowbecauseIG.2connects

backtoIG.1.

FigureFigureFigureFigure6.6.6.6.12121212:Protectioncircuittestedwithinthelaboratory:Protectioncircuittestedwithinthelaboratory:Protectioncircuittestedwithinthelaboratory:Protectioncircuittestedwithinthelaboratory

M3MVR

DPCO



58

6.4ThenewcontrolunitoftheHeenandynamometer6.4ThenewcontrolunitoftheHeenandynamometer6.4ThenewcontrolunitoftheHeenandynamometer6.4ThenewcontrolunitoftheHeenandynamometer

Thenewcontrolgearismountedwithinametallicboxwhichmaybesituatedat

any convenient distance from the dynamometer. Figure 6.13 represents the

upgradedcontrolunitfortheHeenandynamometer.Theboxisearthedtoprovide

an alternative path for a fault current so that the user is protected. All internal

connections are covered withheat shrink so that the user is safe to touchany

internalwireshoweverthisisnotrecommended.Perspexhasbeenusedonthe

topoftheboxforeducationalpurposeandatthesametimetoseethestatusofthe

firingmodule.

Figure6.Figure6.Figure6.Figure6.13

131313::::UUUUpgradedcontrpgradedcontrpgradedcontrpgradedcontrolunit

olunitolunitolunit

As depicted in theabovefigure, theM3MVRand theDPCOare located on the

frontofthecontrolbox.Thisconfigurationallowsanyusertoselectthecontrolling

options offeredbytheM3MVRandatthesame time it allowsthecontrol of the

internalcontactofDPCOrelay.BothrelayaremountedonaDINrailfrominside.

(AppendixFdetailsthedesignofthecontrolunitbox)

M3MVRM3MVRM3MVRM3MVR

DPCODPCODPCODPCO

IndicatorIndicatorIndicatorIndicator(plantisready)

PotentiometerPotentiometerPotentiometerPotentiometer

ResetbuttonResetbuttonResetbuttonResetbutton



59

6666.5Testonthedynamometer.5Testonthedynamometer.5Testonthedynamometer.5Testonthedynamometer

Testingtheupgradedcontrolunitonthedynamometerwasnotachievedbecause

thecontactratingsoftheDPCOrelaywereinappropriateforthisapplication.While

connectingtheupgradedcontrolunittothedynamometer,itwasrealisedthatthe

actualrelay(RL2)connectedtotheignitioncoilwasextremelybigcomparetothe

DPCOrelay.Asa result,itwasassumedthatthenewrelaywillnotwithstandthe

inductivecurrentcomingfromthecoil.

Thecoiloftheengineisoperatedbya20VDCbatterysothatwhenconnection

IG.2isconnectedtoIG.3thecoilcurrentisflowingtroughtheinductor.Therefore,

a magnetic field exists in the region surrounding the inductor. The energy

transferredformtheDCsupplyisnowstoredintheinductor.Consequently,when

theswitchopensthe impedanceacross itincreaseandconsequentlyaveryhigh

voltageisrequiredacrosstheswitchifcurrentistocontinuetoflowtroughit.Asa

resultdamagewillbecausedtotheinternalswitchoftheunderratedrelay.



60

G(s)

Input Output

CHAPTER7–OPENLOOPANDCLOSELOOP

The valve control system has two mode of operation. These two modes of

operation are selected by means of an external selector switch located on the

control desk.When theswitch selects “Governedengines” operatingmode, the

dynamometer acts as an open loop system and when the switch selects

“Ungoverned engines”, the control unit operated as a close loop system. This

chapter describes the open loop configuration of the upgraded control unit and

brieflyexplainshowfeedbackcontrolcanbeachieved.

7.1Theopenloopsystems7.1Theopenloopsystems7.1Theopenloopsystems7.1Theopenloopsystems

Anopenloopsystemisacontrolsystemthatdoesnotuseitsoutputtocorrectthe

process of the system. The system is given a predefined input signal and the

output signal must behave ina predefinedmanner (Nise 2003). Thus, the openloopcontrollerofthedynamometersystemwillessentiallybeapotentiometerthat

willgeneratedifferentlevelofcurrenttothedynamometer’scoil.

FFFFigureigureigureigure7.17.17.17.1OpenloopsystemOpenloopsystemOpenloopsystemOpenloopsystem

Thedesignoftheopenloopofthedynamometersystemcontainsahalfcontrolled

bridge rectifier, a firingmodule and its potentiometer. The bridge rectifier is the

input transducer that converts the main AC source to a DC source. The firing

module isthedevicethatgeneratesthetriggeringgatecurrentata specific time.

Byshiftingthefiringpoint,bymeansofthepotentiometer,thehalfcontrolledbridge



61

rectifierwill produce different levelofexciting current to thedynamometer’s coil.

Consequently,theloadimposedtothecoupledenginewillbedifferentatdifferent

potentiometerposition.Whileoperatingwiththeopenloopsystem,theDCcurrent

flowing in the dynamometer coil is constant irrespective of the dynamometer’s

speed.

7777.2Thecloseloopsystem.2Thecloseloopsystem.2Thecloseloopsystem.2Thecloseloopsystem

Systems thatusea feedbacksignalare called closed-loopcontrol systems.The

reasonforusingfeedbackcontrolwiththedynamometeristoprovideenginespeed

stabilisation.Incasessuchasthetestingofaninternalcombustionengine,speed

stabilisationoftheengineisnecessarytomeasuremanyengineperformancesata

specificspeed.Forexample,whendesigninganengineitisrelevanttoknowhow

much fuels the engine consumes at a specific speed. Similarly, using the

dynamometer to stabilise the speed of the engine facilitates the tunning of the

engine.

To maintain the speed of the engine, the load of the dynamometer must be

adjustedwhenever the enginespeed ischanging.Asexplainedearlier, the load

generated by the dynamometer is proportional to the amount of current flowing

through thefieldcoil.Asa result,speedcontrolcanbeachievedbyvarying the

amountofcurrentgeneratedbytheACtoDCconverter.

InordertoadjusttheDCoutputoftheconverter,theconductionanglehastobe

variedautomaticallyinresponsetoanychangeoftheenginespeed.Inthiscase,

thefeedbacksignalisusedtoadjusttheoutputofthedrivensystem.Themotor

speedismeasuredbymeansofthetachogeneratorandthesignalisfedbacktoa

comparator. The second input signal of the comparator is called the reference

speedsignalandisgeneratedbymeansofacontrollingpotentiometer.



62

The comparator also known as ‘error amplifier’ compares the two signals and

produces an output signal “the error signal”. This signal is dependent on the

difference between the speed reference signal and the feed back signal. A

controller processes this signal in order to reduce the error. The output of the

controller is then processed by the firing module which generates the required

delay angle. As a result, for any change of the engine speed, there will be a

changeinthedynamometerload.

For this application, the most suitable controller would be a proportional plus

integral plus derivative controller (PID). The input of the PID controller is the

differencebetweenthefedbacksignalandthereferencesignal.Ifthefeedback

signalislowerthanthereferencesignal,itmeansthattheengineisrunningbelow

thereferencespeed.Consequently,theloadgeneratedbythedynamometerhasto

be reduced and vice versa. Figure 7.2 represents the close loop system

configurationinordertoachievetheenginespeedstabilisation.

Figure7.2:Figure7.2:Figure7.2:Figure7.2:BBBBlockdiagramthecloseloopsystemlockdiagramthecloseloopsystemlockdiagramthecloseloopsystemlockdiagramthecloseloopsystem



63

7.2.1Thereferencesignal7.2.1Thereferencesignal7.2.1Thereferencesignal7.2.1Thereferencesignal

Thereferencesignalcanbeobtainedbyusingapotentiometerconnectedtothe

fivevoltsDCoutputfromthefiringmodule.Figure7.3showsthefeedbackcontrol

configurationofthetriggeringmodule.

Figure7.3:TriggeringmoduleoutputFigure7.3:TriggeringmoduleoutputFigure7.3:TriggeringmoduleoutputFigure7.3:Triggeringmoduleoutput

Inordertomatchbothsignalstothesamevoltagerange(0–5volts),theoutput

voltageofthetachogeneratorwillhavetobesteppeddownsothatthefeedback

signalwillonlyvariesbetween0and5volts.

7.2.7.2.7.2.7.2.2222ThefeedbacksignalThefeedbacksignalThefeedbacksignalThefeedbacksignal

The tachogeneratorconverts therotationalspeedof the shaft into ananalogue

voltage signal that is processed and used for speed control. However, before

comparingthetachogeneratoroutputagainstthespeedreferencesignal,thefeed

backsignalmust be rectified.Theanaloguesignal can be fed intoa full bridge

rectifierandthenalowpassfiltertoobtainasuitableDCfeedbacksignal.

Lowpassfiltertransferfunctionisdefinedinequation:

sCR 1

1

Vin

Vout

+= (7.1)



64

7.2.3Thedifferenceamplifier7.2.3Thedifferenceamplifier7.2.3Thedifferenceamplifier7.2.3Thedifferenceamplifier

The referencesignaland the feedbacksignalare compared toobtain the error

signalthatwilldrivethecontroller.Themostsuitableamplifierconfigurationforthis

taskisthedifferenceamplifier.

This op amp configuration amplifies the difference between two input voltages

however the ratio of R1/R2 must be equal to the ratio R3/R4 to produce the

requirederrorvoltage.Equation7.2expressesoutputvoltageintermsofR1,R2,

V2andV1.

)12(1

2V V

R

RVout −×= (7.2)

Voutisreferredastheerrorsignal.Figure7.4givesthebasiccircuitconfiguration

ofadifferentialamplifier.

FigureFigureFigureFigure7.7.7.7.4444:D:D:D:Differentialamplifierconfigurationifferentialamplifierconfigurationifferentialamplifierconfigurationifferentialamplifierconfiguration



65

7.2.7.2.7.2.7.2.4444PIDPIDPIDPIDCCCControllerontrollerontrollerontroller

ThePIDcontrolleristhewidelyusedinprocesscontrol.PIDreferstoProportional-

Integral-Derivative, referring to the three terms operating on the error signal to

produceacontrolsignal.Thecontrolsignalisgivenbyequation7.2

∫ ++=dt

)t(dek dt)t(ek )t(ek )t(V di pcontrol

(7.2)

Figure7.5illustratetheuseofaPIDcontrollerinafeedbackcontrolsystem.

Figure7.Figure7.Figure7.Figure7.5555:PIDcontroller:PIDcontroller:PIDcontroller:PIDcontroller

(Source:http://en.wikipedia.org/wiki/Image)

Withtheproportionalcomponent,theerrorismultipliedbyaconstantinorderto

controltheactualerrorsignal.Atthesametime,theerrorsignalisintegratedover

aperiodoftimeandthenmultipliedbyaconstantinorderforthesystemtocorrect

previouserror.Finally,thederivativetermcontrolstheresponsetoachangeinthe

system.



66

With the derivative term the controller can anticipate what action is needed by

estimatingtherateofchangeoftheerrorsignal(Parr1996).Asaresult,whenthe

errorsignalischangingrapidly,thecontrolleraddsmorecorrectiveactionstothe

plant.



67

CHAPTER8–DISCUSIONANDCONCLUSION

8.1AchievementofObjectives8.1AchievementofObjectives8.1AchievementofObjectives8.1AchievementofObjectives

Theaimofthisprojectwastoupgradetheexistingeddy-currentdynamometerby

replacing its current valve operated DC sourcewitha power electronic system.

Mostoftheobjectivesputforwardatthestartofthisprojectwerefulfilled,however,

someofthemchangedduringtheyear.

The protective circuit of the initial circuit was supposed to be re-used with the

upgradedsystem.However,withameticulousanalysisofthecircuitconfigurationit

becameapparentthatthisoptionwasgoingtobetimeconsumingandwouldresult

in a deterioration of the initial control unit. As a result, it was preferable to

disconnecttheentiresystemanddesignthewholecircuitwithupdateddevices.

The first new objective was to upgrade the protection circuit to ensure the

safeguards of the dynamometer. As a result, an updated version of the initial

protection circuit has been designed and tested in the laboratory. The new

protectioncircuitworksperfectlyinthelaboratorybuthasnotbeentestedontothe

dynamometerbecausetheselectedDPCOrelayhasbeenunder-rated.

Aswell as this newobjective, onlyabriefdescriptionof the closed loop control

configurationhasbeeninvestigatedsoastointroducetheconceptofenginespeed

stabilisationtoafuturestudent.



68

8.2FurtherWork8.2FurtherWork8.2FurtherWork8.2FurtherWork

Itwasrealisedthattheselectedrelaywhichisconnectedtotheignitioncoilwas

not suitable for this application. Two propositions were offered to solve this

problem.

The firstwas to use the initial protection circuitwith the upgraded rectifier.This

optionistimeconsumingandwilldegradetheinitialcircuit,however,isarealisable

option.

Thesecondoptionwastorunthevalverectifiercircuitandsensethecurrentfrom

theignitioncoilwhiletheenginewasturnedoffbymeansofRL2(seefigure5.1).

Byknowingthepeakvalueofinductivecurrentwhilethemagneticfieldofthecoil

collapses,awellrateddiodecanbeselectedandthenconnectedinparalleltothe

ignition coil. This diode will act as a free wheeling diode so that the inductive

currentwillremainwithinthecoil.

Chapterseven introducestheclosedloopconfigurationofthesystemandbriefly

explainshowspeedstabilisationcanbeachieved.Thefeedbackcontrolsystem

requiresfurtheranalysisandmoreinvestigationofsystemstabilisation.Asaresult,

thisprojectleadstothedesignoftheclosedloopcontrolsystem.

With furtherwork, the upgraded control unitwill provide two differentmodes of

operation.The firstmodeofoperation,presented in this study,providesmanual

loadcontrol inordertotestandrecordengineperformance.Thesecondmodeof

operationwillenableenginespeedstabilisation.

Inthenearfuture,itwillbepossibletoconnectthecontrolunittoacomputerin

order to acquire digital data. The actual torque measuring apparatus will be

replacedbyaloadcellsothattestdatacanbetransmittedtoadataacquisition

systemratherthanbeingrecordedmanually.



69

8888.3Conclusio.3Conclusio.3Conclusio.3Conclusionnnn

Thisstudyprovidesadescriptionoftheprocess involvedineddycurrentbraking

andmore specifically it defineshow the Heenan dynamometer braking process

occurs.Moreover,thedissertationdescribestheprocessofrectificationandhowit

has been achieved inorder to generate an adjustable DC source froma single

phaseACsource.Also,thepaperprovidesacomprehensivechapteronhowthe

dynamometer,thecontrolunitandtheengineareprotectedandgivesadescription

oftheprotectiondevicesusedintheupgradedprotectivecircuit.Followingthat,a

descriptionofthedevicesselectedforhalfcontrolrectificationisgiven.Thefinal

topicbrieflydescribeshowenginespeedstabilisationcanbeachievedusingthe

openloopsystem.



70

LISTOFREFERENCES Ahfock,T2005,ELE3805PowerElectronicsPrinciples&ApplicationsStudyBook

1&2 ,UniversityofSouthernQueensland,Toowoomba.

Farnell2005,FarnellInoneElectronicEngineering ,APremierFarnellCompany,

NSWAustralia.

Fisher,M1991,Powerelectronic ,PWS–KENT,Boston.

Nise,N2005,ControlSystemsEngineering,Jhonwiley&son,California.

Parr,E1996,ControlEngineering,ButterworthHeinemann,London.

Sharma, R 2005, Electrical Technology Study Book 1 , University of Southern

Queensland,Toowoomba.

Winther, J 1975, Dynamometer Handbook of Basic Theory and Applications ,

Cleveland,Ohio:EatonCorporation.

Williams, B 1992, Devices, Drivers, Applications and passive components ,

MACMILLAN,London.



71

IIIIIIIIIIII APPENDICIESAPPENDICIESAPPENDICIESAPPENDICIES



72

APPENDIXA–PROJECTSPECIFICATION



73



74

APPENDIXB–M3MVRDATASHEET



75



76

APPENDIXC–P102WDATASHEET



77



78



79



80



81



82



83

APPENDIXD–AFM11DATASHEET



84



85



86

APPENDIXE–EQUIPEMENTCOST



87

Name : BAVARIN Rudolph Date : 8/08/2006

Discipline : BENG ELE

Project : 50kW Eddy current Braking

farnell2005

Order

code Part number Description Qty price cost Page178-756 AFM-11 Trigger module 1 273.7 273.68 1/837

351076 CLR11069S5K0K potentiometer 5K 1 35.59 35.59 1/742

890-935 1/4 fine aluminium (grub screw) potentiometer knob 1 6.01 6.01 2/303

362-530 P102W B2HKF config thyristor diode bridge 1 121.3 121.34 1/831

696-547 12VA-12% regulation Transformer Clamp mounting 1 19.28 19.28 2/1016

427-4527 M3MVR Multifunction voltage relay 1 245 245 2/526

443-4470 green SPNO Momentary 1 17.26 17.26 2/752

560-650 DPCO - 5532 series 10 A relay 1 20.12 20.12 2/593

335-4131 double surface 1.15 heat sink 1 42.29 42.29 1/863

Total 780.57



88

APPENDIXF–CONTROLUNITBOXDESIGN



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1 7 0

8.5

4 2 . 0 0 0 4 2 . 0 0 0

2 0

130

46

3 7

37 37 37

1 0 5 4

10

3 1

27.5

2 5

10

2 2

FRONTVIEW



90

3 0

16

7

7

7

7

7

7

BACKVIEW



1 7 5

110

SIDEVIEW

Documents

50kW eddy dynamo.pdf